How to modify array?

Question

I currently have an array of objects where each object has several properties. Example:

[
   { text: 'test1',
     id: 1
   },
   { text: 'test2',
     id: 2
   }
]

What would be the best way to convert this to an array of strings that contains the value from text? I had thought I might be able to do this using underscore.js:

headerText = _.pick(headerRow, 'text');

But I think that since the objects are in an array this will not work. My next idea is to just loop through each element in the array and push the text value to a new array, but i'm curious if anyone knows of a more elegant way to do this? Suggestions?

T.J. Crowder · Accepted Answer · 2013-03-04 16:52:19Z

4

You're looking for Array#map:

var stringArray = headerRow.map(function(entry) {
    return entry.text;
});

Live Example | Source

You don't even need Underscore, Array#map is part of ES5 and fully supported by V8, the JavaScript engine used by Node. Array#map calls the function you give it once for each entry in the array, and builds a new array from the return values of that function.

Or if you want to change the existing array, you can use Array#forEach:

headerRow.forEach(function(entry, index) {
    headerRow[index] = entry.text;
});

Live Example | Source

edited Mar 4, 2013 at 16:52

answered Mar 4, 2013 at 16:45

T.J. Crowder

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Comments

ebsddd · Accepted Answer · 2013-03-04 16:52:57Z

1

Use _.map(headerRow, function(row) { return row.text; }). Array.map isn't available in IE < 9.

edited Mar 4, 2013 at 16:52

answered Mar 4, 2013 at 16:45

ebsddd

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2 Comments

T.J. Crowder Over a year ago

"Array.map isn't available in IE < 9." So? The OP says they're using Node. Node uses V8, which has Array#map.

Abe Miessler Over a year ago

This is node.js (server side javascript) so IE 9 won't be an issue.

Jamie Hutber · Accepted Answer · 2013-03-04 16:46:46Z

0

i'd use a foreach and just loop through it.

 var jamie = [
    { text: 'test1',
      id: 1
    },
    { text: 'test2',
      id: 2
    }
 ];

 var length = jamie.length,
     element = [];
 for (var i = 0; i < length; i++) {
   element[i] = jamie[i].id;
   // Do something with element i.
 }
   console.info(element);

answered Mar 4, 2013 at 16:46

Jamie Hutber

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Comments

Billy Moon · Accepted Answer · 2013-03-04 18:45:55Z

-1

This is a vanilla javascript version, which avoids using the not universally supported Array.map method.

// assign the array to a variable
var a = [
   { text: 'test1',
     id: 1
   },
   { text: 'test2',
     id: 2
   }
];

// loop through each item in the array, reassigning with it's text value
// not like this: for(i in a) a[i] = a[i].text
// but with a for loop based on the array length
var i;
for(i=a.length; i; i--){ a[i-1] = a[i-1].text; }

// check the results
console.log(a);
// ["test1", "test2"]

edited Mar 4, 2013 at 18:45

answered Mar 4, 2013 at 16:46

Billy Moon

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8 Comments

Plato Over a year ago

for(i=0;i<a.length;i++){stringArray.push(row.text)}

Billy Moon Over a year ago

Note: comment seems to have gone linking to why not to use for...in to enumerate arrays

Plato Over a year ago

for i in a could find undesired prototypical stuff

Billy Moon Over a year ago

@T.J.Crowder thanks for the thoughtful insight. I am only coding like this for demonstration here, in my own code, I will add semicolons etc... but I feel that it is more useful to put as little in there that does not directly relate to the question (global declarations / semi-colons/etc..). There was recently an issue with someone copy/pasting my code from stack overflow, causing the stack overflow site to come second in google when searching for stack overflow, so maybe I should start writing more pristine code from now on.

Billy Moon Over a year ago

@T.J.Crowder do you think that there is a problem with the anti-pattern way of using a for-loop? Is it for readability that it is not advised?

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