How do you easily create empty matrices javascript

Question

In python  you can do this      None    9  for x in range 9     and you ll get this     None  None  None  None  None  None  None  None  None     None  None  None  None  None  None  None  None  None     None  None  None  None  None  None  None  None  None     None  None  None  None  None  None  None  None  None     None  None  None  None  None  None  None  None  None     None  None  None  None  None  None  None  None  None     None  None  None  None  None  None  None  None  None     None  None  None  None  None  None  None  None  None     None  None  None  None  None  None  None  None  None     How can I do the equivalent in javascript

User · Answer

Coffeescript to the rescue    1  9  map - gt   1  9  map - gt  null

User · Answer

x000D   x000D     initializing depending on i j  x000D  var M Array from  length 9      i    gt  Array from  length 9      j    gt  i  x  j   x000D   x000D     Print it  x000D   x000D  console table M  x000D     M forEach r   gt  console log r   x000D  document body innerHTML     lt pre gt   M map r   gt  r join   t    join   n    lt  pre gt   x000D     JSON stringify M  null  2     bad for matrices x000D   x000D   x000D    Beware that doing this below  is wrong      var M Array 9  fill        since arrays are sparse    or Array 9  fill Array 9  fill 0     initialization     M 4  4    1    M 3  4  is now 1 too    Because it creates the same reference of Array 9 times  so modifying an item modifies also items at the same index of other rows  since it s the same reference   so you need an additional call to  slice or  map on the rows to copy them  cf torazaburo s answer which fell in this trap   note  It may look like this in the future  with slice-notation-literal proposal  stage 1   const M       1 10  map i   gt      1 10  map j   gt  i  x  j

User · Answer

You can add functionality to an Array by extending its prototype object   Array prototype nullify   function  n         n   n  gt  gt  gt  0      for  var i   0  i  lt  n    i             this  i     null            return this       Then   var arr      nullify 9     or   var arr      nullify 9  map function     return    nullify 9

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This is an exact fix to your problem  but I would advise against initializing the matrix with a default value that represents  0  or  undefined   as Arrays in javascript are just regular objects  so you wind up wasting effort   If you want to default the cells to some meaningful value  then this snippet will work well  but if you want an uninitialized matrix  don t use this version         Generates a matrix  ie  2-D Array  with      m  columns      n  rows     every cell defaulting to  d      function Matrix m  n  d       var mat   Array apply null  new Array m   map          Array prototype valueOf          Array apply null  new Array n   map              function                    return d                                     return mat      Usage    lt  Matrix 3 2  dobon     gt  Array   Array  dobon    dobon    Array  dobon    dobon    Array  dobon    dobon       If you would rather just create an uninitialized 2-D Array  then this will be more efficient than unnecessarily initializing every entry         Generates a matrix  ie  2-D Array  with      m  columns      n  rows     every cell remains  undefined      function Matrix m  n       var mat   Array apply null  new Array m   map          Array prototype valueOf          new Array n             return mat      Usage    lt  Matrix 3 2    gt  Array   Array 2   Array 2   Array 2

User · Answer

var matrix       for var i 0  i lt 9  i          matrix i    new Array 9           or   var matrix       for var i 0  i lt 9  i          matrix i            for var j 0  j lt 9  j              matrix i  j    undefined

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Here s one  no looping    Math pow 10  20      replace   0 g   1   split     map parseFloat     Fill the  20  for length  use the  optional  regexp for handy transforms and map to ensure datatype  I added a function to the Array prototype to easily pull the parameters of  map  into your functions   bit risky  some people strongly oppose touching native prototypes  but it does come in handy        Array prototype  args   function idx            idx     idx   0           return function                 return arguments length  gt  idx   arguments idx    null                        Keys  Math pow 10  20      replace   0 g   1   split     map this  args 1     0  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20      Matrix  Math pow 10  9      replace   0 g   1   split     map this  args 1   map this  args 2

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Array from new Array row        gt  new Array col  fill 0

User · Answer

For a 2-d matrix I d do the following var data   Array 9   9  fill 0   var index    i j    gt  9 i   j    any reference to an index  eg   3 4  can be done as follows data index 3 4      You can replace 9 with any generic ROWS and COLUMNS constants

User · Answer

There is something about Array fill I need to mention   If you just use below method to create a 3x3 matrix   Array 3  fill Array 3  fill 0      You will find that the values in the matrix is a reference       Optimized solution  prevent passing by reference    If you want to pass by value rather than reference  you can leverage Array map to create it   Array 3  fill null  map      gt  Array 3  fill 0

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JavaScript doesn   t have a built-in 2D array concept  but you can certainly create an array of arrays   function createMatrix row  column  isEmpty            let matrix              let array              let rowColumn   row   column         for  let i   1  i  lt   rowColumn  i                  isEmpty    array push        array push i               if  i   column     0                    matrix push array                  array                                      return matrix        createMatrix 5  3  true    or  function createMatrix row  column  from             let  matrix  array                          total   row   column          for  let element   from    1  element  lt   total  element                  array push element              if  element   column     0                    matrix push array                  array                                       return matrix        createMatrix 5  6  1

User · Answer

Array fill  Consider using fill   Array 9  fill   map     gt Array 9  fill      The idea here is that fill   will fill out the items with undefined  which is enough to get map to work on them    You could also fill directly   Array 9  fill Array 9     Alternatives to Array 9  fill   include   Array    Array 9      push    Array 9      concat Array 9   Array from Array 9     We can rewrite the solution a bit more semantically as   function array9     return Array 9  fill      array9   map array9    or  function array n    return Array n  fill      array 9  map      gt  array 9     Array from provides us with an optional second mapping argument  so we have the alternative of writing  Array from Array 9        gt  Array from Array 9      or  if you prefer  function array9 map    return Array from Array 9   map     array9 array9     For verbose description and examples  see Mozilla s Docs on Array prototype fill   here   and for Array from    here     Note that neither Array prototype fill   nor Array from   has support in Internet Explorer  A polyfill for IE is available at the above MDN links   Partitioning  partition Array 81   9    if you have a partition utility handy  Here s a quick recursive one   function partition a  n      return a length    a splice 0  n   concat partition a  n               Looping  We can loop a bit more efficiently with  var a       b  while  a push b        lt  9  while  b push null   lt  9     Taking advantage of the fact that push returns the new array length

User · Answer

With ES6 spread operator  Array 9  fill     Array 9

User · Answer

better  that exactly will work   let mx   Matrix 9  9    function Matrix w  h       let mx   Array w       for let i of mx keys            mx i    Array h       return mx       what was shown  Array 9  fill Array 9       Not correctly working   It does not work  because all cells are fill with one array

User · Answer

Use this function or some like that      function createMatrix line  col  defaultValue   0        return new Array line  fill defaultValue  map  x   gt   return new Array col  fill defaultValue   return x         var myMatrix   createMatrix 9 9

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The question is slightly ambiguous  since None can translate into either undefined or null  null is a better choice   var a       b  var i  j  for  i   0  i  lt  9  i        for  j   0  b       j  lt  9  j          b push null         a push b       If undefined  you can be sloppy and just don t bother  everything is undefined anyway

User · Answer

If you really like one-liners and there is a use for underscore js in your project  which is a great library  you can do write-only things like     range 9  map function n          return   range 9  map function n                return null                  But I would go with standard for-cycle version mentioned above

User · Answer

Well  you can create an empty 1-D array using the explicit Array constructor   a   new Array 9   To create an array of arrays  I think that you ll have to write a nested loop as Marc described

User · Answer

I ll give it my shot as well  var c   Array   for  var i   0  a   c 9   i  lt  9  a i    c 9   i       console log  a join                                                                                                Readable and maintainable

[javascript] How do you easily create empty matrices javascript?

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