Question

If I have the array:

my_array = [{a:3,b:4,c:7},{a:5,b:8,c:6}]
property_names = ["a","c"]

How can use the property_names array against my_array to get the following output?:

subset_array = [[3,7],[5,6]]

Answer 1

var my_array = [{a:3,b:4,c:7}, {a:5,b:8,c:6}];
var keys = ['a', 'c'];

my_array.map(function(d){
    return keys.map(function(k) {
        return d[k];
    });
});

This will give you [[3, 7], [5, 6]] and seems to be just what you want.

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[Obsolete initial answer; before the OP updated his question]

Use o.a and o.c – no magic involved and no kittens harmed!

You could also use the [] syntax: o['a'] and o['c'] – but usually you only use it if you want to access a dynamic property name (i.e. a variable instead of a quotes string inside the [])

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If you want an array with both values:

var a_and_c = [o.a, o.c];

Now you can use a_and_c[0] and [1] to access those two values.