JavaScript: Transforming a multi-dimensional array into a two dimensional array

Question

I have a JS array that's filled with data as follows:

var myarr = [[new Date("2011-12-01"), 389, 380.75, 382.54, 387.93],
[new Date("2011-11-30"), 382.28, 378.3, 381.29, 382.2]...]

Is there some way to only select the entire date column and the last number of each row? I'm looking for an output that's something like this:

[[new Date("2011-12-01"), 387.93],[new Date("2011-11-30"), 382.2]...]

Elliot Bonneville · Accepted Answer · 2012-04-12 12:53:13Z

1

var myCollapsedArr = [[myarr[0][0], myarr[0][myarr[0].length-1]], [myarr[1][0], myarr[1][myarr[1].length-1]];

Or in a for loop:

var myCollapsedArr = [];

for(var i = 0; i<myarr.length; i++) {
    myCollapsedArr.push([myarr[i], [myarr[i][myarr[i].length-1]]);
}

answered Apr 12, 2012 at 12:53

Elliot Bonneville

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2 Comments

Phrogz Over a year ago

Note that it's a good practice to cache the length of your array in the loop setup, otherwise you're re-calculating it every time. Not a big speed hit, but never a bad idea. for (var i=0,len=myarr.length;i<len;++i) …

Zishan Neno Over a year ago

Thanks, Elliot. The loop worked. Although I was thinking that there might be some function such as slice that does it without making use of loops. Cheers!

James Hill · Accepted Answer · 2012-04-12 18:45:17Z

1

Option 1 - Simple for Loop

// Create array to hold new values
var newArray = [];
// Loop through existing array and pull out data
for(var i = 0; i < myarr.length; i++) {
    newArray.push([myarr[i][0], myarr[i][myarr[i].length - 1]]);
}

Here's a working fiddle to demonstrate.

Option 2 - ECMAScript 5 forEach()

// Create array to hold new values
var newArray = [];

// Loop through existing array and pull out data
myarr.forEach(function(obj) {
    newArray.push([obj[0], obj[obj.length - 1]]);
});

Here's a working fiddle to demonstrate.

edited Apr 12, 2012 at 18:45

answered Apr 12, 2012 at 12:54

James Hill

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