I'm trying to find the best way to replace the last N items in an array. I'm thinking of the following:
Remove the N amount of items from the array:
arr = arr.slice(-N);
Add the needed values via array.push() doing an iteration to get to the number of needed insertions like so:
for(var i=0; i<=N; i++) {
arr.push(new value);
}
Is there a more elegant solution to this?
Thanks.
A simple reverse loop would suffice like this:
for(i = arr.length - 1; i >= arr.length - N; i--) {
arr[i] = new_value;
}
i >= arr.length - N since the question asked how to replace the last N items.
Removes and optionally adds values to an array starting and ending at any index value.
example:
var arr = [1, 2, 3, 4];
arr.splice(-1, 1, 'a', 'b', 'c');
A more functional way of doing this would be to use a mixture of slice and concat.
function replaceItemsAtEnd(array, replacements) {
var start = array.slice(0, array.length - replacements.length);
return start.concat(replacements);
}
This has the benefit of not mutating the original array.
Using an array as the replacement items means you aren't limited to replacing with the same value either.
You can use the array .fill() to do this.
var arr = [1, 2, 3, 4, 5, 6];
var N = 3;
var newValue = 0;
arr = arr.fill(newValue, -1 * N);
document.getElementById("output").innerHTML = arr;<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<div id="output"></div>The last N elements are replaced with newValue. Please note: IE and Opera don't support this method, but you can write code that will create the method if its' lacking. See the MDN page on .fill() for the polyfill to add the method if your browser doesn't support it.
Tarun solution was the first one that came to my mind, but I would change it slightly to avoid the situation where array length is smaller than N. So, it becomes:
for(i = arr.length - 1; i>= 0 && N > 0; i--) {
arr[i] = new_value;
N--;
}
How about:
var arr = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'];
var anotherArr = [1, 2, 3];
Array.prototype.splice.apply(arr, [arr.length-anotherArr.length, anotherArr.length].concat(anotherArr));
?
