Mapping an array of objects to key/value pairs in CoffeeScript

I have an array of elements that I would like to apply a mapping to to convert it into key value pairs on a single object (to mimic an associative array).

The approach in Can destructuring assignment be used to effect a projection in CoffeeScript? does not seem to work for me as it results in a simple array instead of key/value pairs.

My language of choice is CoffeeScript or JavaScript.

An example:

[{name: 'a', value: 'b', other: 'c'}, {name: 'd', value: 'e', other: 'f'}]

is supposed to be transformed into:

  a: 'b',
  d: 'e'

One-liners are preferred. ;-)


To fix the syntax error, you'll have to expand { @name: @value } to:

o = {}; o[@name] = @value; o

You can then merge the objects with $.extend() and a splat (with the empty object to avoid accidentally extending jQuery):

$.extend {}, $(row).children('input').map(() -> o = {}; o[@name] = @value; o)...

Though, a simpler option would be just to use a 2-liner:

result = {}
$(row).children('input').each(() -> result[@name] = @value)

var arr = [{name: 'a', value: 'b', other: 'c'}, {name: 'd', value: 'e', other: 'f'}];

var obj = arr.reduce(function ( total, current ) {
    total[ ] = current.value;
    return total;
}, {});

Pure javascript. It's practically a one liner, and it looks hawt.

Array.prototype.reduce is ES5, but isn't difficult to shim. Here's an example shim:

Array.prototype.reduce = function ( fun, initVal ) {
    var sum = initVal || this[ 0 ],
        i = 1, len = this.length;

    do {
        sum = undefined, sum, this[i], i, this );
    } while ( ++i < len );

    return sum;

arr.reduce is a sophisticated version of, which is a sophisticated version of arr.forEach. You can do this for the same effect:

var obj = {};
arr.forEach(function ( val ) {
    obj[ ] = val.value;

//and using jQuery.each
var obj = {};
$.each( arr, function ( index, val ) {
    obj[ ] = val.value;

//latter version in coffeescript:
obj = {}
$.each( arr, (index, val) ->
    obj[ ] = val.value

values = {}
values[name] = value for {name, value} in arr

or in javascript:

var values = {}
    values[] = o.value

Which is almost exactly what the CoffeeScript one compiles to.

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