This question already has an answer here:
I'm trying to create a 6 by 12 Matrix using Array.fill
let m = Array(6).fill(Array(12).fill(0));
While this works, the problem is that the inner Arrays are actually all referencing the same Array
object.
let m = Array(6).fill(Array(12).fill(0));
m[0][0] = 1;
console.log(m[1][0]); // Outputs 1 instead of 0
I wanted (and expected) the value of m[1][0]
to be 0
.
How can I force Array.fill
fill copy-by-values of the given argument (eg: Array(12).fill(0)
is the argument in my case) instead of copying by reference ?
You could use Array.from() instead:
Thanks to Pranav C Balan
in the comments for the suggestion on further improving this.
let m = Array.from({length: 6}, e => Array(12).fill(0));
m[0][0] = 1;
console.log(m[0][0]); // Expecting 1
console.log(m[0][1]); // Expecting 0
console.log(m[1][0]); // Expecting 0
Original Statement (Better optimized above):
let m = Array.from({length: 6}, e => Array.from({length: 12}, e => 0));
You can't do it with .fill()
, but you can use .map()
:
let m = new Array(6).map(function() { return new Array(12); });
edit oh wait that won't work; .map()
won't iterate through the uninitialized elements. You could fill it first:
let m = new Array(6).fill(null).map(function() { return new Array(12); });
You can't do it with Array#fill
method. Instead iterate over the array and add newly created array using a for loop.
let m = Array(6);
for (var i = 0; i < m.length; i++)
m[i] = Array(12).fill(0)
m[0][0] = 1;
console.log(m[1][0]);
来源:https://stackoverflow.com/questions/37949813/array-fillarray-creates-copies-by-references-not-by-value