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/ 6 Years ago, fri, february 9, 2018, 12:00:00
Given an ES6 Map and predicate function, how do I safely delete all non-matching elements for the map?
I could not find an official API function, but I can think of two implementations. The first does not attempt to delete in-place, but instead creates a copy:
// version 1:
function filter(map, pred) {
const result = new Map();
for (let [k, v] of map) {
if (pred(k,v)) {
result.set(k, v);
}
}
return result;
}
const map = new Map().set(1,one).set(2,two).set(3,three);
const even = filter(map, (k,v) => k % 2 === 0);
console.log([...even]); // Output: [ [ 2, 'two' ] ]The other deletes in-place. In my tests, it works but I did not find a guarantee that modifying a map does not break the iterator (of the for-of loop):
// version 2:
function deleteIfNot(map, pred) {
for (let [k, v] of map) {
if (!pred(k,v)) {
map.delete(k);
}
}
return map;
}
const map = new Map().set(1,one).set(2,two).set(3,three);
deleteIfNot(map, (k,v) => k % 2 === 0);
console.log([...map]); // Output: [ [ 2, 'two' ] ]Question:
- Is the second version (the in-place delete) correct on all platforms?
- Is there a better way to implement an in-place filter? Maybe some official API that I missed?
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