QScript Functions for Sort and Delete
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function sortPagesBySignificance(pages_to_sort, log_results, min_p_values) {
includeWeb("QScript Selection Functions"); // for getUserSelections, recursiveGetAll
let fail_message = "Cannot sort the selection. Select two or more pages " +
"in the same folder or at the base level of Pages, or select a single folder of pages.";
let parent; // parent QScript ReportGroup of pages to sort
if (!pages_to_sort) {
user_selections = getAllUserSelections();
let pages_in_same_folder = selectedPageItemsAreInSameFolder(user_selections);
let one_folder_selected = exactlyNSelected(user_selections, "Top Pages", 1);
// Check the user has selected items that can be sorted unambiguously
if (!pages_in_same_folder && !one_folder_selected) {
log(fail_message);
return false;
}
if (pages_in_same_folder && !one_folder_selected) {
parent = user_selections.selected_top_level_pages.length > 0 ? user_selections.selected_top_level_pages[0].parentGroup() : user_selections.selected_items[0].group;
pages_to_sort = user_selections.selected_top_level_pages.concat(user_selections.selected_items);
} else if (one_folder_selected) { // Sort pages within folder
parent = user_selections.selected_top_level_pages[0];
pages_to_sort = parent.subItems.filter(function (item) { return item.type == "ReportGroup" || !item.IsOnPage; });
if (pages_to_sort.length < 1) {
log(fail_message);
return false;
}
}
}else {
parent = pages_to_sort[0].parentGroup();
}
sortItemsBySignificance(pages_to_sort, parent, min_p_values);
// Make a list of pages that don't have sortable objects (tables, plots)
let unsortable_pages = pages_to_sort.filter(function (page) {
if (page.type === "Table" || page.type === "Plot") {
return false;
}
return page.subItems.filter(function (item) {
return ["Table", "Plot"].indexOf(item.type) > -1;
}).length == 0;
});
if (log_results) {
log("Pages have been sorted so that those containing Tables or Charts " +
"with the most significant results (lowest p-values) are at the top.");
}
if (unsortable_pages.length > 0) {
log("Some pages did not contain any tables or charts with " +
"p-values and have been sorted to the bottom.");
}
return;
}
function sortItemsBySignificance(items, parent, min_p_values) {
let sort_objects;
if (min_p_values === undefined) {
sort_objects = items.map((item, idx) => ({item: item,
smallest_p: (item.type === "ReportGroup" ?
getSmallestPValueOnPage(item) :
minimumPValue(item)),
idx: idx}));
} else {
sort_objects = items.map((item, idx) => ({item: item,
smallest_p: min_p_values[idx],
idx: idx}));
}
sort_objects = sort_objects.sort(function (a, b) {
if (a.smallest_p < b.smallest_p) {
return -1;
}
if (a.smallest_p > b.smallest_p) {
return 1;
}
return 0;
});
let previous_item = sort_objects[0].item;
sort_objects.forEach(function (obj, index) {
if (index > 0) {
parent.moveAfter(obj.item, previous_item);
previous_item = obj.item;
}
});
return;
}
// Returns true if all top-level selected pages are in the same folder, otherwise false.
function selectedPagesAreInSameFolder(user_selections) {
var selected_top_level_pages = user_selections.selected_top_level_pages;
var parents = selected_top_level_pages.map(function (page) {
return page.parentGroup();
});
return parents.every(function (grp) { return parents[0].equals(grp)})
}
function selectedPageItemsAreInSameFolder(user_selections) {
var result = true;
var selected_page_items = user_selections.selected_items;
var parents = selected_page_items.map(function (item) {
if (item.group && !item.IsOnPage) {
return item.group.guid;
}
return null;
});
if (parents) {
result = result && parents.every(function (guid) { return parents[0] === guid && guid != null });
}
var selected_top_level_pages = user_selections.selected_top_level_pages;
var page_parents = selected_top_level_pages.map(function (page) {
if (page.parentGroup()) {
return page.parentGroup().guid;
}
return null;
});
if (page_parents) {
result = result && page_parents.every(function (grp) { return parents[0] == grp });
if (parents && parents.length > 0 && page_parents.length > 0) {
result = result && parents[0] === page_parents[0];
}
}
return result;
}
function getSmallestPValueOnPage(page) {
var smallest_p = Infinity;
var tables_plots_on_page = page.subItems.filter(function (item) { return ["Table", "Plot"].indexOf(item.type) > -1; });
tables_plots_on_page.forEach(function(item) {
var min_p = minimumPValue(item);
if (min_p !== undefined && min_p < smallest_p)
smallest_p = min_p;
});
return smallest_p;
}
function minimumPValue(item) {
let row_indices_without_net;
let stats;
let table = item;
// When item is R output it must be
// a visualization with a nested table
// otherwise should not be checked
// and given a value of -Infinity.
// If it has a nested table, then that
// table should be evaluated as any
// other table.
if (item.type == "R Output") {
if (!rItemIsPlot(item))
return -Infinity;
if (rPlotHasNestedTable(item))
table = item.subItems.filter(x => x.type == "Table")[0];
else
return -Infinity; // So as to never delete
}
// treat plots and tables separately
if (item.type == 'Plot') {
if (item.primary == null || item.tertiary != null)
return Infinity;
table = project.report.appendTable();
table.primary = item.primary;
if (item.secondary != null)
table.secondary = item.secondary;
if (item.weight != null)
table.weight = item.weight;
if (item.filters != null)
table.filters = item.filters;
} else if (item.type == "WordCloud")
return Infinity;
if (tableQuestionsHaveNoData(table)) {
return Infinity;
}
// Ensure crosstabs with the same question
// in rows and columns appear at top (so they
// can be easily identified and deleted.
if (table.primary.equals(table.secondary))
return -Infinity;
let pvalues;
try {
pvalues = PValuesExcludingNETs(table);
} catch(e) {
pvalues = Infinity;
}
if (item.type === "Plot")
table.deleteItem(); // Deleting temp table
return minWithReplacedNaN(pvalues, Infinity);
}
function PValuesExcludingNETs(table) {
includeWeb("QScript Table Functions"); // for getStatisticsFromTable
const stat_name = "Corrected p";
let table_output = table.calculateOutput();
row_indices_without_net = table_output.rowIndices(false);
stats = getStatisticsFromTable(table, [stat_name]);
// If there are no p-values, the item is not significant, delete.
if (stats == null || stats[stat_name] == null)
return Infinity;
// remove NET and SUM rows
let pvalues_without_net = [];
row_indices_without_net.forEach(function (index) {
pvalues_without_net.push(stats[stat_name][index]);
});
return pvalues_without_net;
}
function tableQuestionsHaveNoData(table) {
if (table.primary.dataReduction.rowLabels.length == 0)
return true;
if (table.secondary != null && table.secondary.dataReduction != null &&
table.secondary.dataReduction.rowLabels.length == 0)
return true;
return false
}
function sortQuestionsInDataFileOrder(questions) {
var current_data_file = questions[0].dataFile;
var all_question_names = current_data_file.questions.map(function (q) { return q.name; });
questions.sort(function (a, b) {
if (all_question_names.indexOf(a.name) < all_question_names.indexOf(b.name)) { return -1; }
if (all_question_names.indexOf(a.name) > all_question_names.indexOf(b.name)) { return 1; }
return 0;
});
return questions;
}
function sortVariablesInDataFileOrder(variables) {
var current_data_file = variables[0].question.dataFile;
var all_variable_names = current_data_file.variables.map(function (q) { return q.name; });
variables.sort(function (a, b) {
if (all_variable_names.indexOf(a.name) < all_variable_names.indexOf(b.name)) { return -1; }
if (all_variable_names.indexOf(a.name) > all_variable_names.indexOf(b.name)) { return 1; }
return 0;
});
return variables;
}
function deleteInsignificantTablesPlots(p_threshold, log_results, min_p_values) {
includeWeb("QScript Selection Functions"); // for getUserSelections, oneOrMoreSelected
if (log_results === undefined)
log_results = true;
function getThreshold()
{
var sig_level = -1;
while (sig_level <= 0 || sig_level >= 100) {
sig_level = prompt("Please enter the desired significance level (e.g. 95 for significance at 95%):", 95);
}
return Math.round((1 - sig_level/100) * 1e10) / 1e10; // corrected for numerical precision errors
}
const stat_name = 'Corrected p';
const web_mode = inDisplayr();
let selected_items = [];
let deleted_items = [];
let not_evaluated_r_plots = [];
let not_evaluated_r_items = [];
if (web_mode) {
let user_selections = getAllUserSelections();
let organized_selections = organizeSelectedItemsForStatisticBasedDeletion(user_selections);
if (!organized_selections)
return false;
selected_items = organized_selections.selected_items;
not_evaluated_r_plots = organized_selections.not_evaluated_r_plots;
not_evaluated_r_items = organized_selections.not_evaluated_r_items;
} else {
selected_items = selectedTablesAndPlots(project.report);
if (selected_items.length < 1) {
log("There are no tables or charts selected. Select one or more tables or charts.");
return false;
}
}
if (p_threshold == null)
p_threshold = getThreshold();
if (min_p_values == null)
min_p_values = selected_items.map(minimumPValue);
// filter selected_items with significant p-values, leaving only items for deletion
deleted_items = selected_items.filter((item,idx) => {
p = min_p_values[idx];
return p > p_threshold;
});
let not_deleted = selected_items.filter((item,idx) => {
p = min_p_values[idx];
return p <= p_threshold;
});
// In Q, just delete the selected items. On the web we need to clear out the pages
// which are made blank by the removal of tables/plots
// This is mainly to facilitate the Insert > Report feature being cleanable.
let all_selected_pages = deleted_items.map(item => item.IsOnPage ? item.group : item);
let previous_page = identifyPreviousPageToDeletions(all_selected_pages);
let deleted_table_names = [];
let deleted_plot_names = [];
deleted_items.forEach(function (item) {
try {
(item.type === "Table" ? deleted_table_names : deleted_plot_names).push(item.name);
item.deleteItem();
return;
} catch (e) {}
});
let deleted_page_names = [];
if (web_mode) {
deleted_page_names = deleteEmptyPages(all_selected_pages.filter(item => item && item.type == "ReportGroup"));
}
if (log_results && !web_mode)
logDeletionSummary(deleted_table_names, deleted_plot_names,
deleted_page_names, min_p_values, p_threshold);
if (deleted_items.length > 0) {
if (not_deleted.length > 0) {
let target_item = web_mode ? not_deleted[0].group : not_deleted[0];
project.report.setSelectedRaw([target_item]);
} else
project.report.setSelectedRaw([previous_page]);
}
if (not_evaluated_r_plots.length > 0)
log("Some visualizations could not be evaluated for significance and have not been deleted.");
if (not_evaluated_r_items.length > 0)
log(correctTerminology("Calculations were not evaluated for significance and have not been deleted."));
return;
}
function deleteEmptyPages(pages) {
// for recursiveGetAllGroupsInGroup, recursiveGetAllItemsInGroup
includeWeb("QScript Selection Functions");
let deleted_pages = [];
let deleted_page_names = [];
pages.forEach(function (x) {
recursiveGetAllGroupsInGroup(x , pages);
});
pages.forEach(function (page) {
var current_sub_items = [];
recursiveGetAllItemsInGroup(page, current_sub_items);
current_sub_items = current_sub_items.filter(item => item.type != "Text");
if (current_sub_items.length === 0) {
deleted_pages.push(page);
deleted_page_names.push(page.name);
}
});
deleted_pages.forEach(function (page) {
try {
page.deleteItem();
} catch (e) {
}
})
return deleted_page_names;
}
function logDeletionSummary(deleted_table_names, deleted_plot_names,
deleted_page_names, min_p_values, p_threshold) {
let n_deleted = deleted_table_names.length + deleted_plot_names.length;
if (n_deleted === 0) {
log("No tables or plots met the condition to be deleted.");
return;
}
if (deleted_table_names.length > 0) {
log('The following tables were not significant at the ' + p_threshold +
' level, and have been deleted:');
log(deleted_table_names.join("\r\n"));
log('\r\n');
}
if (deleted_plot_names.length > 0) {
log('The following plots were not significant at the ' + p_threshold + ' level, and have been deleted:');
log(deleted_plot_names.join("\r\n"));
log('\r\n');
}
if (deleted_page_names.length > 0) {
log('The following pages were made empty, and have been deleted:');
log(deleted_page_names.join("\r\n"));
}
return;
}
function sortPagesAlphabetically() {
includeWeb("QScript Functions to Generate Outputs");
includeWeb('QScript Selection Functions');
includeWeb('QScript Table Functions');
includeWeb('QScript Utility Functions');
var fail_message = "Cannot sort the selection. Select two or more pages/outputs in the same folder or at the base level of Pages, or select a single folder.";
var user_selections = getAllUserSelections();
var pages_in_same_folder = selectedPageItemsAreInSameFolder(user_selections);
var one_folder_selected = exactlyNSelected(user_selections, "Top Pages", 1);
// Check the selected pages are not length 0
if (user_selections.selected_top_level_pages.length == 0 && user_selections.selected_items.length == 0) {
log(fail_message);
return false;
}
// Check the user has selected items that can be sorted unambiguously
if (!pages_in_same_folder && !one_folder_selected) {
log(fail_message);
return false;
}
// Sort selected pages
var parent;
var pages_to_sort;
if (pages_in_same_folder) {
parent = user_selections.selected_top_level_pages.length > 0 ? user_selections.selected_top_level_pages[0].parentGroup() : user_selections.selected_items[0].group;
pages_to_sort = user_selections.selected_top_level_pages.concat(user_selections.selected_items);
} else if (one_folder_selected) { // Sort pages within folder
parent = user_selections.selected_top_level_pages[0];
pages_to_sort = parent.subItems.filter(function (item) { return item.type == "ReportGroup" || !item.IsOnPage; });
if (pages_to_sort.length < 1) {
log(fail_message);
return false;
}
}
pages_to_sort.sort(function (a, b) {
if (a.name.toLowerCase() < b.name.toLowerCase()) { return -1; }
if (a.name.toLowerCase() > b.name.toLowerCase()) { return 1; }
return 0;
});
var last_page = pages_to_sort[0];
pages_to_sort.forEach(function (page, index) {
if (index > 0) {
parent.moveAfter(page, last_page);
last_page = page;
}
});
}
/** Sorts the selected variable sets or variables alphabetically. */
function sortVariablesAlphabetically(by_variable_name = false) {
includeWeb("QScript Selection Functions");
function getSortableName(x, by_variable_name) {
if (x.type == "Question")
return by_variable_name ? x.variables[0].name : x.name;
else
return by_variable_name ? x.name : x.label;
}
var fail_message = "Cannot sort. Select two or more individual variables, or at least one variable set, under Data Sets.";
var user_selections = getAllUserSelections();
var selected_questions = user_selections.selected_questions;
if (!NOrMoreSelected(user_selections, "Variable", 2)) {
log(fail_message);
return false;
}
if (!exactlyNSelected(user_selections, "Data Set", 1)) {
log("Cannot sort. Select variables from one data set only.");
return false;
}
var data_file = user_selections.selected_data_sets[0];
// Sort variable sets First
// Only if more than one is selected
if (NOrMoreSelected(user_selections, "Question", 2)) {
var selected_questions = user_selections.selected_questions;
// Move variables together.
sortQuestionsInDataFileOrder(selected_questions);
var last_variable = selected_questions[0].variables[selected_questions[0].variables.length - 1];
var remaining_questions = selected_questions.slice(1);
var remaining_variables = [];
remaining_questions.forEach(function (q) {
remaining_variables = remaining_variables.concat(q.variables);
});
data_file.moveAfter(remaining_variables, last_variable);
// Sort questions by name
selected_questions.sort(function (a, b) {
let a_name = getSortableName(a, by_variable_name).toLowerCase();
let b_name = getSortableName(b, by_variable_name).toLowerCase();
if (a_name < b_name) { return -1; }
if (a_name > b_name) { return 1; }
return 0;
});
var last_variable = selected_questions[0].variables[selected_questions[0].variables.length - 1];
selected_questions.forEach(function (q, index) {
if (index > 0) {
data_file.moveAfter(q.variables, last_variable);
last_variable = q.variables[q.variables.length - 1];
}
});
} else if (exactlyNSelected(user_selections, "Question", 1)) {
// If a single variable set is selected, sort the variables within it
// or if a subset of variables is selected, sort them relative to
// one another.
let question = user_selections.selected_questions[0];
let selected_variables = user_selections.selected_variables.slice(0);
if (selected_variables.length < 2) {
return;
}
let question_index_in_file = question.dataFile.questions.findIndex(q => q.guid === question.guid);
let last_var = null;
if (question_index_in_file > -1) {
let previous_question = question.dataFile.questions[question_index_in_file - 1];
last_var = previous_question.variables[previous_question.variables.length - 1];
}
// Selected variables are in the order of selection, so we need to find the smallest variable index in the variable set
const selected_indices = selected_variables.map(selected_var => question.variables.findIndex(v => v.guid === selected_var.guid)).filter(i => i > -1);
if (selected_indices.length <= 0) {
log('Could not find the selected variables in the variable set.');
return;
}
const selected_first_variable_index = Math.min(...selected_indices);
// Sort selected variables alphabetically by label
selected_variables.sort(function (a, b) {
let a_name = getSortableName(a, by_variable_name).toLowerCase();
let b_name = getSortableName(b, by_variable_name).toLowerCase();
if (a_name < b_name) { return -1; }
if (a_name > b_name) { return 1; }
return 0;
});
const reordered_all_variables = question.variables.slice(0);
let index = selected_first_variable_index;
// move sorted selected variables to be together
for (let i = 0; i < selected_variables.length; i++, index++) {
reordered_all_variables[index] = selected_variables[i];
}
// move the rest variables
for (let i = selected_first_variable_index; i < question.variables.length; i++) {
const variable = question.variables[i];
if (selected_variables.findIndex(v => v.guid === variable.guid) < 0) {
reordered_all_variables[index] = variable;
index++;
}
}
question.dataFile.moveAfter(reordered_all_variables, last_var);
}
}
function organizeSelectedItemsForStatisticBasedDeletion(user_selections) {
let selected_items = [];
let not_evaluated_r_plots = [];
let not_evaluated_r_items = [];
// Check selections
if (!(oneOrMoreSelected(user_selections, "Table", true) ||
oneOrMoreSelected(user_selections, "Plot", true) ||
oneOrMoreSelected(user_selections, "WordCloud", true) ||
oneOrMoreSelected(user_selections, "R Output", true))) {
log("There are no tables or charts selected. Select one or more " +
"pages which contain tables or charts.");
return false;
}
selected_items = [].concat(user_selections.selected_tables).concat(user_selections.selected_plots).concat(user_selections.selected_word_clouds);
selected_items = selected_items.concat(user_selections.implicitly_selected_tables)
.concat(user_selections.implicitly_selected_plots)
.concat(user_selections.implicitly_selected_word_clouds);
// Special handling for R outputs.
// Can currently only check significance for R plots that have nested
// tables (i.e. have been converted from a table).
// Do not delete any other R items and later tell the user that those
// items could not be check and were not deleted.
let selected_r_items = user_selections.implicitly_selected_r_outputs;
// Separate plots from other R items
let r_plots_vs_other = splitArrayIntoApplicableAndNotApplicable(selected_r_items, rItemIsPlot);
not_evaluated_r_items = r_plots_vs_other.notApplicable;
let selected_r_plots = r_plots_vs_other.applicable;
// Separate plots which have nested tables from those that don't
let r_plots_can_evaluate = splitArrayIntoApplicableAndNotApplicable(selected_r_plots, rPlotHasNestedTable);
not_evaluated_r_plots = r_plots_can_evaluate.notApplicable;
// Include R plots with nested tables among things to check
selected_items = selected_items.concat(selected_r_plots);
return { selected_items: selected_items,
not_evaluated_r_plots: not_evaluated_r_plots,
not_evaluated_r_items: not_evaluated_r_items }
}
function deleteWithSmallSample() {
let min_size = prompt("Please enter the minimum sample size that you wish to view. Tables and visualizations with a smaller sample size will be removed.", 10);
const stat_name = 'Base n';
const web_mode = inDisplayr();
let selected_items = [];
let not_evaluated_r_plots = [];
let not_evaluated_r_items = [];
if (web_mode) {
let user_selections = getAllUserSelections();
let organized_selections = organizeSelectedItemsForStatisticBasedDeletion(user_selections);
if (!organized_selections)
return false;
selected_items = organized_selections.selected_items;
not_evaluated_r_plots = organized_selections.not_evaluated_r_plots;
not_evaluated_r_items = organized_selections.not_evaluated_r_items;
selected_items = selected_items.filter(item => item.group != null);
} else {
selected_items = selectManyTablesWithGroupNames("Please choose which tables you would like to check. Tables with a sample size less than " +min_size+" will be removed." , project.report).tables;
if (selected_items.length < 1) {
log("There are no tables or charts selected. Select one or more tables or charts.");
return false;
}
}
let deleted_items = [];
let not_deleted_items = [];
selected_items.forEach(function (item) {
if (maxBaseBelowThreshhold(item, min_size))
deleted_items.push(item);
else
not_deleted_items.push(item);
});
// In Q, just delete the selected items. On the web we need to clear out the pages
// which are made blank by the removal of tables/plots
// This is mainly to facilitate the Insert > Report feature being cleanable.
let all_selected_pages = deleted_items.map(item => item.group);
let previous_page = identifyPreviousPageToDeletions(all_selected_pages);
let deleted_table_names = [];
let deleted_plot_names = [];
deleted_items.forEach(function (item) {
try {
(item.type === "Table" ? deleted_table_names : deleted_plot_names).push(item.name);
item.deleteItem();
return;
} catch (e) {}
});
let deleted_page_names = [];
if (web_mode) {
deleted_page_names = deleteEmptyPages(all_selected_pages);
}
// If we have deleted anything, choose where to change the focus
if (deleted_items.length > 0) {
if (not_deleted_items.length > 0) {
let target_item = web_mode ? not_deleted_items[0].group : not_deleted_items[0];
project.report.setSelectedRaw([target_item]);
} else
project.report.setSelectedRaw([previous_page]);
}
if (!web_mode) {
if (deleted_table_names.length > 0) {
log("The following tables have been removed: ");
log(deleted_table_names.join('\r\n'));
} else {
log("No tables were found to have a sample size less than " + min_size +".");
}
}
if (not_evaluated_r_plots.length > 0)
log("Sample size could not be identified for some visualizations and these have not been deleted.");
if (not_evaluated_r_items.length > 0)
log(correctTerminology("Sample size was not checked for Calculations and these have not been deleted."));
return;
}
// Identify whether the largest sample size for an item
// is below the given min size.
// For tables, check the Base n.
// For plots, convert to table and check the Base n
// For visualizations with nested tables, check the base n
// of the nested table.
// For other R items, do nothing.
function maxBaseBelowThreshhold(item, min_size) {
let output;
let table;
if (item.type == 'Table') {
try {
output = item.calculateOutput();
} catch (e) {
return true; // Table is empty and should be removed
}
if (output.availableStatistics.indexOf('Text') > -1)
return false; // Table is text and does not have concept of missing data
return maxWithReplacedNaN(output.get('Base n'), 0) < min_size;
}
if (item.type == 'Plot') {
if (item.primary == null)
return true; // empty, delete
if (item.tertiary != null)
return false; //can't check sample size on this, don't delete
table = project.report.appendTable();
table.primary = item.primary;
if (item.secondary != null)
table.secondary = item.secondary;
if (item.weight != null)
table.weight = item.weight;
if (item.filters != null)
table.filters = item.filters;
try {
output = table.calculateOutput();
let delete_this = maxWithReplacedNaN(output.get('Base n'), 0) < min_size;
table.deleteItem();
return delete_this;
} catch (e) {
table.deleteItem();
return true; // plot is empty and should be removed
}
}
if (item.type == "R Output") {
if (!rItemIsPlot(item))
return false; // not a plot, don't delete
if (rPlotHasNestedTable(item)) {
table = item.subItems.filter(x => x.type == "Table")[0];
try {
output = table.calculateOutput();
return maxWithReplacedNaN(output.get('Base n'), 0) < min_size;
} catch (e) {
return true; // Table is empty and should be removed
}
} else
return false; // not nested table, don't delete
}
}
// Given a collection of pages to be deleted, work out what page
// is previous to those pages to which the focus can be set at the
// completion of the QScript
function identifyPreviousPageToDeletions(deleted_pages) {
let previous_page = null;
if (deleted_pages.length > 0) {
let parent_of_first = deleted_pages[0].group;
if (parent_of_first) {
let guids_in_parent = parent_of_first.subItems.filter(x => x.type == "ReportGroup" || !x.IsOnPage)
.map(y => y.guid);
let index_of_first_within_parent = guids_in_parent.indexOf(deleted_pages[0].guid);
if (index_of_first_within_parent == 0)
previous_page = parent_of_first;
else
previous_page = parent_of_first.subItems[index_of_first_within_parent - 1];
}
}
return previous_page;
}