Multi-dimensional associative arrays in JavaScript

Question

There is the following query results   key1 and key2 could be any text   id   key1     key2     value  1    fred     apple    2 2    mary     orange   10 3    fred     banana   7 4    fred     orange   4 5    sarah    melon    5       and I wish to store the data in a grid  maybe as an array  looping all the records like this            apple    orange   banana  melon fred        2        4         7     - mary        -        10        -     - sarah       -        -         -     5   In PHP this would be really easy  using associative arrays    result  fred    apple     2    But in JavaScript associative arrays like this doesn t work  After reading tons of tutorial  all I could get was this   arr     arr 1   apple     2    but arr  fred    apple     2  doesn t work  I tried arrays of objects  but objects properties can t be free text  The more I was reading tutorials  the more I got confused     Any idea is welcome

User · Answer

Javascript is flexible   var arr        fred     apple   2   orange   4      mary          etc  etc     alert arr fred orange   alert arr  fred    orange     for  key in arr fred      alert key          arr fred key

User · Answer

It appears that for some applications  there is a far simpler approach to multi dimensional associative arrays in javascript    Given that the internal representation of all arrays are actually as objects of objects  it has been shown that the access time for numerically indexed elements is actually the same as for associative  text  indexed elements    the access time for first-level associative indexed elements does not rise as the number of actual elements increases    Given this   there may be many cases where it is actually better to use a concatenated string approach to create the equivalence of a multidimensional elements    For example   store  fruit    apples    granny    price    10 store  cereal    natural    oats    quack     20   goes to   store  fruit apples granny price     10 store  cereal natural oats quack     20   Advantages include    no need to initialize sub-objects or figure out how to best combine objects  single-level access time   objects within objects need N times the access time can use Object keys   to extract all dimension information and   can use the function regex test string  and the array map function on the keys to pull out exactly what you want  no hierarchy in the dimensions  the  dot  is arbitrary - using underscore actually makes regex easier there are lots of scripts for  flattening  JSON into and out of this format as well can use all of the other nice array processing functions on keylist

User · Answer

Don t use an array  use an object   var foo   new Object

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Just use a regular JavaScript object  which would  read  the same way as your associative arrays   You have to remember to initialize them first as well   var obj        obj  fred         if  fred  in obj         can check for the presence of  fred  if obj fred         also checks for presence of  fred  if obj  fred           also checks for presence of  fred      The following statements would all work obj  fred    apples     1  obj fred apples   1  obj  fred   apples   1      or build or initialize the structure outright var obj     fred    apples  1  oranges  2    alice    lemons  1        If you re looking over values  you might have something that looks like this   var people     fred    alice    var fruit     apples    lemons     var grid       for var i   0  i  lt  people length  i         var name   people i       if name in grid    false           grid name           must initialize the sub-object  otherwise will get  undefined  errors            for var j   0  j  lt  fruit length  j             var fruitName   fruit j           grid name  fruitName    0

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x000D   x000D   lt script language  javascript  gt  x000D   x000D     Set values to variable x000D  var sectionName    TestSection   x000D  var fileMap    fileMapData   x000D  var fileId    foobar   x000D  var fileValue   foobar png   x000D  var fileId2    barfoo   x000D  var fileValue2   barfoo jpg   x000D   x000D     Create top-level image object x000D  var images       x000D   x000D     Create second-level object in images object with x000D     the name of sectionName value x000D  images sectionName        x000D   x000D     Create a third level object x000D  var fileMapObj       x000D   x000D     Add the third level object to the second level object x000D  images sectionName  fileMap    fileMapObj  x000D   x000D     Add forth level associate array key and value data x000D  images sectionName  fileMap  fileId    fileValue  x000D  images sectionName  fileMap  fileId2    fileValue2  x000D   x000D   x000D     All variables x000D  alert   Example 1 Value      images sectionName  fileMap  fileId    x000D   x000D     All keys with dots x000D  alert   Example 2 Value      images TestSection fileMapData foobar   x000D   x000D     Mixed with a different final key x000D  alert   Example 3 Value      images sectionName   fileMapData   fileId2    x000D   x000D     Mixed brackets and dots    x000D  alert   Example 4 Value      images sectionName   fileMapData   barfoo   x000D   x000D     This will FAIL  variable names must be in brackets  x000D  alert   Example 5 Value      images sectionName   fileMapData   fileId2   x000D     Produces   Example 5 Value  undefined   x000D   x000D     This will NOT work either  Values must be quoted in brackets  x000D  alert   Example 6 Value      images sectionName  fileMapData  barfoo   x000D     Throws and exception and stops execution with error  fileMapData is not defined x000D   x000D     We never get here because of the uncaught exception above    x000D  alert   The End     x000D   lt  script gt  x000D   x000D   x000D

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var myObj           myObj  Base             myObj  Base    Base panel panel base      ContextParent    ClassParent    NameParent    Context  Base  Class  panel  Name  panel base  Visible    ValueIst    ValueSoll                                                   Align      AlignFrom    AlignTo    Content    onClick    Style    content ger sie    content ger du    content eng           myObj  Base    Base panel panel top       ContextParent    ClassParent    NameParent    Context  Base  Class  panel  Name  panel base  Visible    ValueIst    ValueSoll                                                   Align    AlignFrom    AlignTo    Content    onClick    Style    content ger sie    content ger du    content eng            myObj  SC1             myObj  SC1    Base panel panel base      ContextParent    ClassParent    NameParent    Context  Base  Class  panel  Name  panel base  Visible    ValueIst    ValueSoll                                                   Align      AlignFrom    AlignTo    Content    onClick    Style    content ger sie    content ger du    content eng           myObj  SC1    Base panel panel top       ContextParent    ClassParent    NameParent    Context  Base  Class  panel  Name  panel base  Visible    ValueIst    ValueSoll                                                   Align    AlignFrom    AlignTo    Content    onClick    Style    content ger sie    content ger du    content eng             console log myObj        if   Base  in myObj          console log  Base found           if   Base panel panel base  in myObj  Base               console log  Base panel panel base found             console log  old value      myObj  Base    Base panel panel base   Context           myObj  Base    Base panel panel base      new Value         console log  new value      myObj  Base    Base panel panel base                     Output    Base found  Base panel panel base found   old value  Base   new value  new Value   The array operation works  There is no problem   Iteration        Object keys myObj  Base    forEach function key  index                        var value   objcons  Base   key                               myObj

User · Answer

If it doesn t have to be an array  you can create a  quot multidimensional quot  JS object     lt script type  quot text javascript quot  gt  var myObj          fred    apples  2  oranges  4  bananas  7  melons  0         mary    apples  0  oranges  10  bananas  0  melons  0         sarah    apples  0  oranges  0  bananas  0  melons  5       document write myObj  fred    apples      lt  script gt

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As I needed get all elements in a nice way I encountered this SO subject  Traversing 2 dimensional associative array object  - no matter the name for me  because functionality counts   var imgs pl           offer             img    wer-handwritter 03 png    left   1   top   2         portfolio         img    wer-handwritter 10 png    left   1   top   2         special           img    wer-handwritter 15 png    left   1   top   2      for  key in imgs pl         console log key       for  subkey in imgs pl key              console log imgs pl key  subkey

User · Answer

Get the value for an array of associative arrays's property when the property name is an integer:

Starting with an Associative Array where the property names are integers:

var categories = [
    {"1":"Category 1"},
    {"2":"Category 2"},
    {"3":"Category 3"},
    {"4":"Category 4"}
];

Push items to the array:

categories.push({"2300": "Category 2300"});
categories.push({"2301": "Category 2301"});

Loop through array and do something with the property value.

for (var i = 0; i < categories.length; i++) {
    for (var categoryid in categories[i]) {
        var category = categories[i][categoryid];
        // log progress to the console
        console.log(categoryid + " : " + category);
        //  ... do something
    }
}

Console output should look like this:

1 : Category 1
2 : Category 2
3 : Category 3
4 : Category 4
2300 : Category 2300
2301 : Category 2301

As you can see, you can get around the associative array limitation and have a property name be an integer.

NOTE: The associative array in my example is the json you would have if you serialized a Dictionary[] object.

User · Answer

You don t need to necessarily use Objects  you can do it with normal multi-dimensional Arrays   This is my solution without Objects      Javascript const matrix        matrix key1        value1      value2       matrix key2        value3        which in PHP is equivalent to      PHP  matrix          key1    gt             value1            value2               key2    gt             value3

[javascript] Multi-dimensional associative arrays in JavaScript

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