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Arrays of Data

Arrays of objects are a common data format in JavaScript database connectors and other general data sources.

Numeric datasets commonly use arrays of arrays of numbers.

The "Data Storage" section gives a general overview of common array formats in JavaScript.

The "Functions" section describes the related functions.

Data Storage​

Array of Arrays​

The spiritual equivalent of the grid in JavaScript is an array of arrays:

SpreadsheetArray of Arrays

pres.xlsx data

[
["Name", "Index"],
["Bill Clinton", 42],
["GeorgeW Bush", 43],
["Barack Obama", 44],
["Donald Trump", 45],
["Joseph Biden", 46]
]

Each array within the structure corresponds to one row. Individual data points can be read by indexing by row index and by column index:

var aoa = [
["Name", "Index"],
["Bill Clinton", 42],
["GeorgeW Bush", 43],
["Barack Obama", 44],
["Donald Trump", 45],
["Joseph Biden", 46]
];

var value_at_B4 = aoa[3][1]; // 44
var value_at_A2 = aoa[1][0]; // Bill Clinton

Arrays of Objects​

Arrays of objects are commonly used to represent rows from a database:

SpreadsheetArray of Objects

pres.xlsx data

[
{ Name: "Bill Clinton", Index: 42 },
{ Name: "GeorgeW Bush", Index: 43 },
{ Name: "Barack Obama", Index: 44 },
{ Name: "Donald Trump", Index: 45 },
{ Name: "Joseph Biden", Index: 46 }
]

Each object within the structure corresponds to one data row. The first row of the spreadsheet is interpreted as the header row.

Functions​

The "Input" subsections describe functions that generate SheetJS worksheet objects from arrays of data.

The "Array Output" subsection defines functions that extract data from SheetJS worksheet objects.

Example Sheet​

The live examples are based on the following worksheet:

SheetJS
12 567
23 678
34 789
4567890

This table includes duplicate column labels ("e" and "S" appear twice in the first row) and gaps (three data rows have missing fields).

Array of Arrays Input​

Create a worksheet from an array of arrays

var ws = XLSX.utils.aoa_to_sheet(aoa, opts);

XLSX.utils.aoa_to_sheet takes an array of arrays of JS values and returns a worksheet resembling the input data. Values are interpreted as follows:

  • Numbers, Booleans and Strings are stored as the corresponding types.
  • Date objects are stored as Date cells or date codes (see cellDates option)
  • Array holes and explicit undefined values are skipped.
  • null values may be stubbed (see sheetStubs and nullError options)
  • Cell objects are used as-is.

The function takes an options argument:

Option NameDefaultDescription
dateNFFMT 14Use specified date format in string output
cellDatesfalseStore dates as type d (default is n)
sheetStubsfalseCreate cell objects of type z for null values
nullErrorfalseIf true, emit #NULL! error cells for null values
UTCfalseIf true, dates are interpreted using UTC methods **
densefalseEmit dense sheets

UTC option is explained in "Dates"

The following live example reproduces the example worksheet:

function SheetJSExportAOA() {
/* array of arrays of data */
var aoa = [
["S", "h", "e", "e", "t", "J", "S"],
[ 1, 2, , , 5, 6, 7],
[ 2, 3, , , 6, 7, 8],
[ 3, 4, , , 7, 8, 9],
[ 4, 5, 6, 7, 8, 9, 0]
];
return ( <button onClick={() => {
/* create worksheet */
var ws = XLSX.utils.aoa_to_sheet(aoa);
/* create workbook and export */
var wb = XLSX.utils.book_new();
XLSX.utils.book_append_sheet(wb, ws, "Sheet1");
XLSX.writeFile(wb, "SheetJSExportAOA.xlsx");
}}>Click to export Array of Arrays</button> );
}

Add data from an array of arrays to an existing worksheet

XLSX.utils.sheet_add_aoa(ws, aoa, opts);

XLSX.utils.sheet_add_aoa takes an array of arrays of JS values and updates an existing worksheet object. It follows the same process as aoa_to_sheet and accepts an options argument:

Option NameDefaultDescription
dateNFFMT 14Use specified date format in string output
cellDatesfalseStore dates as type d (default is n)
sheetStubsfalseCreate cell objects of type z for null values
nullErrorfalseIf true, emit #NULL! error cells for null values
originUse specified cell as starting point (see below)
UTCfalseIf true, dates are interpreted using UTC methods **

UTC option is explained in "Dates"

origin is expected to be one of:

originDescription
(cell object)Use specified cell (cell object)
(string)Use specified cell (A1-Style cell)
(number >= 0)Start from the first column at specified row (0-indexed)
-1Append to bottom of worksheet starting on first column
(default)Start from cell A1

The example worksheet can be built up in the following order:

SpreadsheetOperations
SheetJS
12 567
23 678
34 789
4567890
  1. aoa_to_sheet([[]]) creates an empty worksheet

  2. sheet_add_aoa writes A1:G1 (red)

  3. sheet_add_aoa writes A2:B4 (blue)

  4. sheet_add_aoa writes E2:G4 (green)

  5. sheet_add_aoa writes A5:G5 (yellow)

/* Start from an empty worksheet */
var ws = XLSX.utils.aoa_to_sheet([[]]);

/* First row */
XLSX.utils.sheet_add_aoa(ws, [ "SheetJS".split("") ], {origin: "A1"});

/* Write data starting at A2 */
XLSX.utils.sheet_add_aoa(ws, [[1,2], [2,3], [3,4]], {origin: "A2"});

/* Write data starting at E2 */
XLSX.utils.sheet_add_aoa(ws, [[5,6,7], [6,7,8], [7,8,9]], {origin:{r:1, c:4}});

/* Append row */
XLSX.utils.sheet_add_aoa(ws, [[4,5,6,7,8,9,0]], {origin: -1});
function SheetJSAddAOA() { return ( <button onClick={() => {
/* Start from an empty worksheet */
var ws = XLSX.utils.aoa_to_sheet([[]]);

/* First row */
XLSX.utils.sheet_add_aoa(ws, [ "SheetJS".split("") ], {origin: "A1"});

/* Write data starting at A2 */
XLSX.utils.sheet_add_aoa(ws, [[1,2], [2,3], [3,4]], {origin: "A2"});

/* Write data starting at E2 */
XLSX.utils.sheet_add_aoa(ws, [[5,6,7], [6,7,8], [7,8,9]], {origin:{r:1, c:4}});

/* Append row */
XLSX.utils.sheet_add_aoa(ws, [[4,5,6,7,8,9,0]], {origin: -1});

/* create workbook and export */
var wb = XLSX.utils.book_new();
XLSX.utils.book_append_sheet(wb, ws, "Sheet1");
XLSX.writeFile(wb, "SheetJSAddAOA.xlsx");
}}>Click to export Array of Arrays</button> ); }

Array of Objects Input​

Create a worksheet from an array of objects

var ws = XLSX.utils.json_to_sheet(aoo, opts);

XLSX.utils.json_to_sheet takes an array of objects and returns a worksheet with automatically-generated "headers" based on the keys of the objects. The default column order is determined by the first appearance of the field using Object.keys. The function accepts an options argument:

Option NameDefaultDescription
headerUse specified field order (default Object.keys) **
dateNFFMT 14Use specified date format in string output
cellDatesfalseStore dates as type d (default is n)
skipHeaderfalseIf true, do not include header row in output
nullErrorfalseIf true, emit #NULL! error cells for null values
UTCfalseIf true, dates are interpreted using UTC methods **
densefalseEmit dense sheets

UTC option is explained in "Dates"

All fields from each row will be written! header hints at a particular order but is not exclusive. To remove fields from the export, filter the data source.

Some data sources have special options to filter properties. For example, MongoDB will add the _id field when finding data from a collection:

const aoo_with_id = await coll.find({}).toArray();
const ws = XLSX.utils.json_to_sheet(aoo_with_id); // includes _id column

This can be filtered out through the projection property:

const aoo = await coll.find({}, {projection:{_id:0}}).toArray(); // no _id !
const ws = XLSX.utils.json_to_sheet(aoo);

If a data source does not provide a filter option, it can be filtered manually:

const aoo = data.map(obj => Object.fromEntries(Object.entries(obj).filter(r => headers.indexOf(r[0]) > -1)));
  • If header is an array, missing keys will be added in order of first use.
  • Cell types are deduced from the type of each value. For example, a Date object will generate a Date cell, while a string will generate a Text cell.
  • Null values will be skipped by default. If nullError is true, an error cell corresponding to #NULL! will be written to the worksheet.
function SheetJSExportAOO() {
/* array of arrays of data */
var aoo = [
{ Name: "Bill Clinton", Index: 42 },
{ Name: "GeorgeW Bush", Index: 43 },
{ Name: "Barack Obama", Index: 44 },
{ Name: "Donald Trump", Index: 45 },
{ Name: "Joseph Biden", Index: 46 }
];
return ( <button onClick={() => {
/* create worksheet */
var ws = XLSX.utils.json_to_sheet(aoo);
/* create workbook and export */
var wb = XLSX.utils.book_new();
XLSX.utils.book_append_sheet(wb, ws, "Sheet1");
XLSX.writeFile(wb, "SheetJSExportAOO.xlsx");
}}>Click to export Array of Objects</button> );
}

The example sheet cannot be reproduced using plain objects since JS object keys must be unique.

Typically the original data source will have different column names. After writing with json_to_sheet, the aoa_to_sheet method can rewrite the headers:

/* original array of objects */
var data = [
{ S:1, h:2, t:5, J:6, S_1:7 },
{ S:2, h:3, t:6, J:7, S_1:8 },
{ S:3, h:4, t:7, J:8, S_1:9 },
{ S:4, h:5, e:6, e_1:7, t:8, J:9, S_1:0 },
];

/* column order for the generated worksheet */
// | A | B | C | D | E | F | G |
var data_headers = [ "S", "h", "e", "e_1", "t", "J", "S_1" ];

/* new headers for the first row of the worksheet */
// | A | B | C | D | E | F | G |
var new_headers = [ "S", "h", "e", "e", "t", "J", "S" ];

/* write data with using data headers */
var ws = XLSX.utils.json_to_sheet(data, { header: data_headers });

/* replace first row */
XLSX.utils.sheet_add_aoa(worksheet, [new_headers], { origin: "A1" });

Add data from an array of objects to an existing worksheet

XLSX.utils.sheet_add_json(ws, aoo, opts);

XLSX.utils.sheet_add_json takes an array of objects and updates an existing worksheet object. It follows the same process as json_to_sheet and accepts an options argument:

Option NameDefaultDescription
headerUse specified column order (default Object.keys)
dateNFFMT 14Use specified date format in string output
cellDatesfalseStore dates as type d (default is n)
skipHeaderfalseIf true, do not include header row in output
nullErrorfalseIf true, emit #NULL! error cells for null values
originUse specified cell as starting point (see below)
UTCfalseIf true, dates are interpreted using UTC methods **

UTC option is explained in "Dates"

origin is expected to be one of:

originDescription
(cell object)Use specified cell (cell object)
(string)Use specified cell (A1-Style cell)
(number >= 0)Start from the first column at specified row (0-indexed)
-1Append to bottom of worksheet starting on first column
(default)Start from cell A1

This example worksheet can be built up in the order A1:G1, A2:B4, E2:G4, A5:G5:

/* Start from an empty worksheet */
var ws = XLSX.utils.aoa_to_sheet([[]]);

/* Header order */
var header = ["A", "B", "C", "D", "E", "F", "G"];

/* First row */
XLSX.utils.sheet_add_json(ws, [
{ A: "S", B: "h", C: "e", D: "e", E: "t", F: "J", G: "S" }
], {header: header, skipHeader: true});

/* Write data starting at A2 */
XLSX.utils.sheet_add_json(ws, [
{ A: 1, B: 2 }, { A: 2, B: 3 }, { A: 3, B: 4 }
], {header: header, skipHeader: true, origin: "A2"});

/* Write data starting at E2 */
XLSX.utils.sheet_add_json(ws, [
{ A: 5, B: 6, C: 7 }, { A: 6, B: 7, C: 8 }, { A: 7, B: 8, C: 9 }
], {header: ["A", "B", "C"], skipHeader: true, origin: { r: 1, c: 4 }});

/* Append row */
XLSX.utils.sheet_add_json(ws, [
{ A: 4, B: 5, C: 6, D: 7, E: 8, F: 9, G: 0 }
], {header: header, skipHeader: true, origin: -1});

If the header option is an array, sheet_add_json and sheet_to_json will append missing elements.

This design enables consistent header order across calls:

function SheetJSHeaderOrder() {
/* Use shared header */
const header = [];
const ws1 = XLSX.utils.json_to_sheet([ {C: 2, D: 3}, ], {header});
XLSX.utils.sheet_add_json(ws1, [ {D: 1, C: 4}, ], {header, origin: -1, skipHeader: true});

/* only use header in first call */
const ws2 = XLSX.utils.json_to_sheet([ {C: 2, D: 3}, ], {header:[]});
XLSX.utils.sheet_add_json(ws2, [ {D: 1, C: 4}, ], {origin: -1, skipHeader: true});

return (<pre>
<b>Objects</b>
{"\n[\n { C: 2, D: 3 },\n { D: 1, C: 4 } // different key order\n]\n"}<br/>
<b>Worksheet when same `header` array is passed to `sheet_add_json`</b>
<div dangerouslySetInnerHTML={{__html:XLSX.utils.sheet_to_html(ws1)}}/>
<i>New contents of `header`</i><br/>
{JSON.stringify(header)}<br/>
<br/>
<b>Worksheet when no `header` property is passed to `sheet_add_json`</b>
<div dangerouslySetInnerHTML={{__html:XLSX.utils.sheet_to_html(ws2)}}/>
</pre>)
}

Array Output​

var arr = XLSX.utils.sheet_to_json(ws, opts);

var aoa = XLSX.utils.sheet_to_json(ws, {header: 1, ...other_opts});

XLSX.utils.sheet_to_json generates an array of JS objects. The function takes an options argument:

Option NameDefaultDescription
rawtrueUse raw values (true) or formatted strings (false)
range**Override Range (see table below)
headerControl output format (see table below)
dateNFFMT 14Use specified date format in string output
defvalUse specified value in place of null or undefined
blankrows**Include blank lines in the output **
skipHiddenfalseDo not generate objects for hidden rows/columns
UTCfalseIf true, dates will be correct in UTC **
  • raw only affects cells which have a format code (.z) field or a formatted text (.w) field.
  • If header is specified, the first row is considered a data row; if header is not specified, the first row is the header row and not considered data.
  • When header is not specified, the conversion will automatically disambiguate header entries by affixing _ and a count starting at 1. For example, if three columns have header foo the output fields are foo, foo_1, foo_2
  • null values are returned when raw is true but are skipped when false.
  • If defval is not specified, null and undefined values are skipped normally. If specified, all null and undefined points will be filled with defval
  • When header is 1, the default is to generate blank rows. blankrows must be set to false to skip blank rows.
  • When header is not 1, the default is to skip blank rows. blankrows must be true to generate blank rows
  • UTC option is explained in "Dates"

range is expected to be one of:

rangeDescription
(number)Use worksheet range but set starting row to the value
(string)Use specified range (A1-Style bounded range string)
(default)Use worksheet range (ws['!ref'])

header is expected to be one of:

headerDescription
1Generate an array of arrays
"A"Row object keys are literal column labels
array of stringsUse specified strings as keys in row objects
(default)Read and disambiguate first row as keys
  • If header is not 1, the row object will contain the non-enumerable property __rowNum__ that represents the row of the sheet corresponding to the entry.
  • If header is an array, the keys will not be disambiguated. This can lead to unexpected results if the array values are not unique!

For the example worksheet:

function SheetJSToJSON() {
/* original data */
var ws = XLSX.utils.aoa_to_sheet([
["S", "h", "e", "e", "t", "J", "S"],
[ 1, 2, , , 5, 6, 7],
[ 2, 3, , , 6, 7, 8],
[ 3, 4, , , 7, 8, 9],
[ 4, 5, 6, 7, 8, 9, 0]
]);

/* display JS objects with some whitespace */
const aoo = o => o.map(r => " " + JSON.stringify(r).replace(/,"/g, ', "').replace(/:/g, ": ").replace(/"([A-Za-z_]\w*)":/g, '$1:')).join("\n");
const aoa = o => o.map(r => " " + JSON.stringify(r).replace(/,/g, ', ').replace(/null/g, "")).join("\n");

return ( <pre>
<b>Worksheet (as HTML)</b>
<div dangerouslySetInnerHTML={{__html: XLSX.utils.sheet_to_html(ws)}}/>
<b>XLSX.utils.sheet_to_json(ws, {'{'} header: 1 {'}'}) [array of arrays]</b><br/>
[<br/>{aoa(XLSX.utils.sheet_to_json(ws, { header: 1 }))}<br/>]<br/><br/>
<b>XLSX.utils.sheet_to_json(ws) [objects with header disambiguation]</b><br/>
[<br/>{aoo(XLSX.utils.sheet_to_json(ws))}<br/>]<br/><br/>
<b>XLSX.utils.sheet_to_json(ws, {'{'} header: "A" {'}'}) [column names as keys]</b><br/>
[<br/>{aoo(XLSX.utils.sheet_to_json(ws, { header: "A" }))}<br/>]<br/><br/>
<b>XLSX.utils.sheet_to_json(ws, {'{'} header: ["A","E","I","O","U","6","9"] {'}'})</b><br/>
[<br/>{aoo(XLSX.utils.sheet_to_json(ws, { header: ["A","E","I","O","U","6","9"] }))}<br/>]<br/>
</pre> );
}