Declare an empty two-dimensional array in Javascript

Question

I want to create a two dimensional array in Javascript where I m going to store coordinates  x y   I don t know yet how many pairs of coordinates I will have because they will be dynamically generated by user input   Example of pre-defined 2d array   var Arr   1 2   3 4   5 6      I guess I can use the PUSH method to add a new record at the end of the array    How do I declare an empty two dimensional array so that when I use my first Arr push   it will be added to the index 0  and every next record written by push will take the next index   This is probably very easy to do  I m just a newbie with JS  and I would appreciate if someone could write a short working code snippet that I could examine  Thanks

User · Answer

If we don   t use ES2015 and don   t have fill    just use  apply    See https   stackoverflow com a 47041157 1851492   x000D   x000D  let Array2D    r  c  fill    gt  Array apply null  new Array r   map function    return Array apply null  new Array c   map function    return fill     x000D   x000D  console log JSON stringify Array2D 3 4 0     x000D  console log JSON stringify Array2D 4 5 1     x000D   x000D   x000D

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You can just declare a regular array like so   var arry         Then when you have a pair of values to add to the array  all you need to do is   arry push  value 1  value2      And yes  the first time you call arry push  the pair of values will be placed at index 0   From the nodejs repl    gt  var arry       undefined  gt  arry push  1 2    1  gt  arry     1  2      gt  arry push  2 3    2  gt  arry     1  2      2  3       Of course  since javascript is dynamically typed  there will be no type checker enforcing that the array remains 2 dimensional  You will have to make sure to only add pairs of coordinates and not do the following    gt  arry push 100   3  gt  arry     1  2        2  3      100

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If you want to initialize along with the creation  you can use fill and map   const matrix   new Array 5  fill 0  map      gt  new Array 4  fill 0      5 is the number of rows and 4 is the number of columns

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You can try something like this -  var arr   new Array        Push data   arr 0  0     abc xyz

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const grid   Array from Array 3   e   gt  Array 4      Array from arrayLike  mapfn   mapfn is called  being passed the value undefined  returning new Array 4    An iterator is created and the next value is repeatedly called  The value returned from next  next   value is undefined  This value  undefined  is then passed to  the newly-created array s iterator  Each iteration s value is undefined  which you can see if you log it   var grid2   Array from Array 3   e   gt      console log e      undefined   return Array 4      a new Array

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One line solution  var x   3  y   4   var ar   new Array x  fill new Array y  fill 0     It creates matrix array with values   0

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You can fill an array with arrays using a function     var arr       var rows   11  var columns   12   fill2DimensionsArray arr  rows  columns    function fill2DimensionsArray arr  rows  columns       for  var i   0  i  lt  rows  i              arr push  0           for  var j   0  j  lt  columns  j                  arr i  j    0                        The result is     Array 11  0  12   0  0  0  0  0  0  0  0  0  0  0  0  1  12   0  0  0  0  0  0  0  0  0  0  0  0  2  12   0  0  0  0  0  0  0  0  0  0  0  0  3  12   0  0  0  0  0  0  0  0  0  0  0  0  4  12   0  0  0  0  0  0  0  0  0  0  0  0  5  12   0  0  0  0  0  0  0  0  0  0  0  0  6  12   0  0  0  0  0  0  0  0  0  0  0  0  7  12   0  0  0  0  0  0  0  0  0  0  0  0  8  12   0  0  0  0  0  0  0  0  0  0  0  0  9  12   0  0  0  0  0  0  0  0  0  0  0  0  10  12  0  0  0  0  0  0  0  0  0  0  0  0

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I know this is an old thread but I d like to suggest using an array of objects rather than an array of arrays  I think it make the code simpler to understand and update   x000D   x000D     Use meaningful variable names like  points       anything better than a bad pirate joke   arr   var points           Create an object literal  then add it to the array var point    x  0  y  0   points push point       Create and add the object to the array in 1 line points push  x 5  y 5        Create the object from local variables  var x   10  var y   8  points push  x  y        Ask the user for a point too var response   prompt  Please enter a coordinate point  Example  3 8    var coords   response split      map Number   points push  x  coords 0   y  coords 1         Show the results var canvas   document getElementById  graph    var painter   canvas getContext  2d    var width   canvas width  height   canvas height  var scale   10  radius   3 5  deg0   0  deg360   2   Math PI   painter beginPath    for  var point of points        var x   point x   scale   scale      var y   height - point y   scale - scale      painter moveTo x   radius  y       painter arc x  y  radius  deg0  deg360       painter fillText    point x     point y    x   radius   1  y   radius   1     painter stroke    x000D   lt canvas id  graph  width  150  height  150  style  border  1px solid red   gt  lt  canvas gt  x000D   x000D   x000D

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What s wrong with   var arr2   new Array 10 20       arr2 0 0    5      arr2 0 1    2     console log  sum is        arr2 0 0     arr2 0 1      should read out  sum is 7

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No need to do so much of trouble  Its simple   This will create 2   3 matrix of string   var array     var x   2  y   3  var s    abcdefg    for var i   0  i lt x  i         array i  new Array          for var j   0  j lt y  j              array i  push s charAt counter

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x000D   x000D  var arr       x000D  var rows   3  x000D  var columns   2  x000D   x000D  for  var i   0  i  lt  rows  i      x000D      arr push         creates arrays in arr x000D    x000D  console log  elements of arr are arrays     x000D  console log arr   x000D   x000D  for  var i   0  i  lt  rows  i      x000D      for  var j   0  j  lt  columns  j      x000D          arr i  j    null     empty 2D array  it doesn t make much sense to do this x000D        x000D    x000D  console log    x000D  console log  empty 2D array     x000D  console log arr   x000D   x000D  for  var i   0  i  lt  rows  i      x000D      for  var j   0  j  lt  columns  j      x000D          arr i  j    columns   i   j   1  x000D        x000D    x000D  console log    x000D  console log  2D array filled with values     x000D  console log arr   x000D   x000D   x000D

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ES6 Matrix m with size 3 rows and 5 columns  remove  fill 0  to not init by zero      Array 3   map x  gt Array 5  fill 0            x000D   x000D  let Array2D    r c    gt      Array r   map x  gt Array c  fill 0     let m   Array2D 3 5    m 1  0    2      second row  first column m 2  4    8      last row  last column     print formated array console log JSON stringify m     replace                   g    n    2  n    replace     g     n        x000D   x000D   x000D

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for 3 x 5 array      new Array 3  fill new Array 5  fill 0

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An empty array is defined by omitting values  like so   v         a    b  1 2  a push b  b  a 0

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You can nest one array within another using the shorthand syntax       var twoDee

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We usually know the number of columns but maybe not rows  records   Here is an example of my solution making use of much of the above here   For those here more experienced in JS than me - pretty much everone - any code improvement suggestions welcome        var a cols    null null null null null null null null null        var a rxc      a cols             just checking  var arr    a rxc length     Array isArray a rxc           alert   a rxc length     arr    Returned 1          Quick test of array to check can assign new rows to a rxc           i can be treated as the rows dimension and  j the columns          for  i 0  i lt 3  i                for  j 0  j lt 9  j                  a rxc i  j    i j              alert   i     i    j     j           a rxc i  j                            if  i 1 lt 3    a rxc i 1      a cols                  And if passing this array to the sever the ajax that works for me is      post     ajax myservercode php                    jqArrArg1   a onedimarray          jqArrArg2   a rxc                  function        text             done function srvresp status        id PageContainer   html srvresp                fail function jqXHR status    alert  jqXHR AJAX error     jqXHR     gt  gt     status

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Create an object and push that object into an array   var jSONdataHolder   function country  lat  lon         this country   country      this lat   lat      this lon   lon     var jSONholderArr        jSONholderArr push new jSONdataHolder  Sweden    60    17     jSONholderArr push new jSONdataHolder  Portugal    38    9     jSONholderArr push new jSONdataHolder  Brazil    23    -46      var nObj   jSONholderArr length  for  var i   0  i  lt  nObj  i         console log jSONholderArr i  country          jSONholderArr i  lat              jSONholderArr i  lon

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If you want to be able access the matrix like so matrix i  j   I find it the most convinient to init it in a loop   var matrix           cols   3     init the grid matrix for   var i   0  i  lt  cols  i           matrix i             this will give you                      so      matrix 0  0      matrix 1  0  return undefined and not the error  Uncaught TypeError  Cannot set property  0  of undefined

[javascript] Declare an empty two-dimensional array in Javascript?

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