If I have an array, what's a simple way of selecting non-consecutive elements? The second and fifth elements for example:
a = ["a","b","c","d","e"]
a.select_elements([1,4]) // should be ["b","e"]
EDIT
I just realized I can do [1,4].map(function(i) {return a[i]}). Is there a less verbose way?
If you're looking for something to make your code look shorter, you could extend Array to have this method:
Array.prototype.select_elements = function(indices) {
var elements = [];
for (var i=0; i != indices.length; ++i)
elements.push(this[indices[i]]);
return elements;
}
Now you can call the method you want:
a.select_elements([1,4])
["b", "e"]
arguments object. Though yours matches the code concept in the question.
create a new array, with the elements manually:
var select_elements = [a[1], a[4]];
or create a function that constructs a new array from indices:
function selectElementsWithIndices(sourceArray, selectIndices)
{
var result = new Array();
for ( var i = 0; i < selectIndices; i++ ) {
var index = selectIndices[i];
result.push(sourceArray[index]);
}
return result;
}
var select_elements = selectElementsWithIndices(a, [1, 4]);
You can safely (will not show up in for loops) add a function to all arrays:
Object.defineProperty(Array.prototype, 'get', {
__proto__: null,
value: function() {
return Array.prototype.slice.call(arguments).map(function(index){ return this[index] }.bind(this));
}
})
Usage:
a = [1, 2, 3, 4, 5, 6];
a.get(1, 4);
Non-variadic version:
Object.defineProperty(Array.prototype, 'get', {
__proto__: null,
value: function(indices) {
return indices.map(function(index){ return this[index] }.bind(this));
}
})
Usage:
a = [1, 2, 3, 4, 5, 6];
a.get([1, 4]);
There's nothing built in. You can do this:
a.select_elements([a[1], a[4]]);
...which constructs a new array, uses the elements a[1] and a[4], and then passes that to the a.select_elements function.
var {1:x, 4:y} = a;, which will set thexandyvariables to the1and4members..prototypeof the appropriate constructor, so you could write a simple method like:a.grab(1,4)that will return a new Array with those members.