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trunc.js
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trunc.js
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import deque from '@aureooms/js-collections-deque';
import {iter} from './iter.js';
import {take} from './take.js';
/**
* Yields all elements of the iterable except the last <code>n</code> ones. If
* <code>n</code> is negative, behaves like <code>{@link take}( iterable, -n
* )</code>.
*
* @example
* // returns [ 0 , 1 , 2 ]
* list( trunc( range( 5 ) , 2 ) ) ;
*
* @param {Iterable} iterable - The input iterable.
* @param {Number} n - The number of elements to exclude from the output.
* @returns {Iterator}
*/
export function* trunc(iterable, n) {
if (n < 0) {
yield* take(iterable, -n);
return;
}
if (n === 0) {
yield* iterable;
return;
}
const iterator = iter(iterable);
const buffer = deque(null, n);
while (n-- > 0) {
const event = iterator.next();
if (event.done) {
return;
}
buffer.append(event.value);
}
for (const value of iterator) {
yield buffer.popleft();
buffer.append(value);
}
}