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]]
-
2To get better answers you should provide some more context: Why do you need a subset of array elements and how are the needed properties determined?Sirko– Sirko2012-05-14 14:48:46 +00:00Commented May 14, 2012 at 14:48
-
@nachocab Update the post itself.user166390– user1663902012-05-14 14:50:41 +00:00Commented May 14, 2012 at 14:50
-
@nachocab: Can you create a complete example with input values and the output you expect?ThiefMaster– ThiefMaster2012-05-14 14:55:55 +00:00Commented May 14, 2012 at 14:55
Add a comment
|
3 Answers
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.
[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 [])
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.
6 Comments
gdoron
Come on, Show us a magic! like access
a and c at the very same time! Or extract a kitten from the object.
nachocab
is there a way not to add them manually? what if I have a hundred properties in the object?
apsillers
Do you want to loop over all the property keys of the object? Use a
for(key in object) loop.nachocab
I just want to loop over a few of the keys. These are specified in a separate array
ThiefMaster
@nachocab: Updated my answer. This seems to be what you are looking for.
|
You can access the properties by two notations:
Either o.a and o.c or o['a'] and o['c'].
EDIT
If you want to create a new array containing both values, then just do so using, e.g, the code suggested by @Reid :
[o.a, o.c]
2nd EDIT
So just build your array up inside the map function like the following:
var filter = [ "a","c","f","zzz"]; // should
subset_array = my_array.map( function(v){ var newArr = [];
for( var i=0; i<filter.length; ++i ) {
if ( typeof v[ filter[i] ] !== 'undefined' ) {
newArr.push( v[ filter[i] ] );
}
}
return newArr;
} );
One thing to note is, however, that as long as you use primitive types (like the int values in the example) the above code will clone the properties. This means, if you change a value in my_array at some point, subset_array will not be changed implicitly, but you have to recreate subset_array or adjust the value there, too.
1 Comment
nachocab
how can I get them both in an array, at the same time [5,6]?
This is not a full answer, however I believe it will be of use:
var values = []
var obj = {a: 1, b: 2, c: 3}
for (var prop in obj) {
if (obj.hasOwnValue(prop)) { // skip props in [[prototype]], no effect here
values.push(obj[prop])
}
}
values // -> [2, 1, 3] (in SOME UNDEFINED ORDER)
Key points:
- Iterate [all] object property names for the object (but not [[prototype]] chain)
- Access value dynamically from property name
- Properties are not ordered; sort
valuesif needed, for instance
This can be expanded to add different "exclusion" rules, for instance. It can also be adapted to different higher-order functions.
Happy coding.
Comments
