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In Javascript, given a simple number[]
array, is there an elegant way to calculate the minimum and maximum values simultaneously, or return undefined
if the array is empty?
Something like this:
const a = [1, 2, 3];
const (min, max) = minMax(a);
Pre-emptive response notes:
This is not a duplicate of this question because he is not actually calculating the min and max of the same array, but the min or max of 4 different arrays.
I want to calculate these in one pass. Not
[Math.min(a), Math.max(a)]
.I know how to do the obvious way:
let min = undefined;
let max = undefined;
for (const x of array) {
min = min === undefined ? x : Math.min(min, x);
max = max === undefined ? x : Math.max(max, x);
}
I am wondering if there is something a bit more elegant, e.g. using Array.reduce()
.
In Javascript, given a simple number[]
array, is there an elegant way to calculate the minimum and maximum values simultaneously, or return undefined
if the array is empty?
Something like this:
const a = [1, 2, 3];
const (min, max) = minMax(a);
Pre-emptive response notes:
This is not a duplicate of this question because he is not actually calculating the min and max of the same array, but the min or max of 4 different arrays.
I want to calculate these in one pass. Not
[Math.min(a), Math.max(a)]
.I know how to do the obvious way:
let min = undefined;
let max = undefined;
for (const x of array) {
min = min === undefined ? x : Math.min(min, x);
max = max === undefined ? x : Math.max(max, x);
}
I am wondering if there is something a bit more elegant, e.g. using Array.reduce()
.
-
there is no
Math.reduce
function, do you meanArray.reduce
? And if so, just put yourfor of
loop in thereduce
function and you're done. – pretzelhammer Commented Jun 24, 2020 at 13:58 -
Ah yeah oops, thanks! And it isn't as simple as that because the input and output of
reduce
have to be the same type. I could doarray.map(x => [x, x]).reduce(...)
but euurgh. Not my idea of elegant. – Timmmm Commented Jun 24, 2020 at 14:00 -
array.reduce(([min,max], x)=>[Math.min(min,x),Math.max(max,x)],[,,].fill(array[0]))
? – user120242 Commented Jun 24, 2020 at 14:09
4 Answers
Reset to default 6You can use Array.reduce()
to reduce into any kind of result, it doesn't have to be the same type. For example, reducing an array of numbers into an output array of two numbers, min and max:
const minMax = arr =>
arr.reduce(([min,max=min],num) => [Math.min(num,min),Math.max(num,max)], arr);
const a = [5,2,6,3,3,1,1];
const [min,max] = minMax(a);
console.log("min",min,"max",max);
The reduce
is seeded with the array itself, for brevity and because anything else is somewhat unnecessary. This would mess up arrays of length 1 due to the destructuring, so max=min
is used to set max
equal to the first element as a fallback. So cases of array length 1 or 0 are handled.
Using Array.reduce
and only iterating over the array once. I'm using array destructing assignment to pass back both min
and max
values from the function (since JS doesn't have tuple types). I'm also checking for the edge cases of the array being empty:
function minMax(array) {
if (array.length == 0) {
return [undefined, undefined];
}
return array.reduce(([min, max], val) => {
return [Math.min(min, val), Math.max(max, val)];
}, [Number.MAX_VALUE, Number.MIN_VALUE]);
}
function testMinMax(array) {
let [min, max] = minMax(array);
console.log(min, max);
}
testMinMax([]); // logs "undefined undefined"
testMinMax([1]); // logs "1 1"
testMinMax([1, 2, 3, 4, 5]); // logs "1 5"
With spread operator bining with Math.min and Math.max
const a = [1, 2, 3];
const [min, max] = [Math.min(...a), Math.max(...a)];
console.log({min, max});
Why not just this:
function minMax(arr) {
arr = arr.sort((a, b) => a - b);
return [arr.at(0), arr.at(-1)]
}
const a = [1, 2, 3];
const [ min, max ] = minMax(a);
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