One would anticipate that Array#slice should be at least as efficient as the other alternatives, if not faster. While it involves a temporary duplication of memory, with 1M numbers only occupying about 64MB of memory, the additional 32MB for the desired elements is quite affordable:
array = array.slice(500000);
Moreover, this approach prevents the JavaScript engine from resorting to object usage instead of arrays internally. Additionally, exploring the use of Float64Array for floats may be beneficial as it ensures optimized arrays and prevents potential performance degradation that can occur when deleting array entries.
An initial NodeJS experiment indicates that slice is significantly faster than splice, with Float64Array showing near-identical results to untyped arrays in the slice scenario:
"use strict";
let sliceStats = createStats();
let sliceTypedStats = createStats();
let spliceStats = createStats();
for (let c = 0; c < 100; ++c) {
if (test(buildUntyped, sliceStats, testSlice).length != 500000) throw new Error("1");
if (test(buildTyped, sliceTypedStats, testSlice).length != 500000) throw new Error("2");
if (test(buildUntyped, spliceStats, testSplice).length != 500000) throw new Error("3");
console.log(c);
}
console.log("slice ", avg(sliceStats.sum, sliceStats.count));
console.log("sliceTyped", avg(sliceTypedStats.sum, sliceTypedStats.count));
console.log("splice ", avg(spliceStats.sum, spliceStats.count));
function avg(sum, count) {
return (sum / count).toFixed(3);
}
function createStats() {
return {
count: 0,
sum: 0
};
}
function buildUntyped() {
let a = [];
for (let n = 0; n < 1000000; ++n) {
a[n] = Math.random();
}
return a;
}
function buildTyped() {
let a = new Float64Array(1000000);
for (let n = 0; n < 1000000; ++n) {
a[n] = Math.random();
}
return a;
}
function test(build, stats, f) {
let a;
let ignore = 0;
let start = Date.now();
for (let i = 0; i < 10; ++i) {
let s = Date.now();
a = build();
ignore += Date.now() - s;
a = f(a);
}
stats.sum += Date.now() - start - ignore;
++stats.count;
return a;
}
function testSlice(a) {
return a.slice(500000);
}
function testSplice(a) {
a.splice(0, 500000);
return a;
}