From the Wikipedia page cited: As with quicksort, quickselect is generally implemented as an in-place algorithm, and beyond selecting the kth element,

From the Wikipedia page cited: As with quicksort, quickselect is generally implemented as an in-place algorithm, and beyond selecting the kth element, it also partially sorts the data. When the above is applicable, those quickselect implementations would violate the original assertion of: Only the median (or pair around the median) needs to be sorted, the other numbers can be unsorted When the collection involved is immutable.