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selectperm

selectperm(v, k, [alg=,] [by=,] [lt=,] [rev=false])

Return a partial permutation of the the vector v, according to the order specified by by, lt and rev, so that v[output] returns the first k (or range of adjacent values if k is a range) values of a fully sorted version of v. If k is a single index (Integer), an array of the first k indices is returned; if k is a range, an array of those indices is returned. Note that the handling of integer values for k is different from select in that it returns a vector of k elements instead of just the k th element. Also note that this is equivalent to, but more efficient than, calling sortperm(...)[k]

Examples

julia> v = [5, 2, 8, 3, 1];
julia> selectperm(v, 3)
3-element Array{Int64,1}:
 5
 2
 8

In this example, the selectperm function is used to obtain a partial permutation of the vector v, where the first 3 elements of a fully sorted version of v are selected.

julia> v = [5, 2, 8, 3, 1];
julia> selectperm(v, 2:4)
3-element Array{Int64,1}:
 2
 3
 1

This example demonstrates the usage of selectperm with a range 2:4 as the second argument. It returns an array of indices corresponding to the elements in v that would be selected if the range 2:4 were applied to a fully sorted version of v.

julia> v = [5, 2, 8, 3, 1];
julia> selectperm(v, 2, rev=true)
2-element Array{Int64,1}:
 8
 5

In this example, the rev=true argument is used to obtain a partial permutation of the vector v in reverse order. The first 2 elements of a fully sorted version of v are selected and returned in reverse order.

julia> v = [5, 2, 8, 3, 1];
julia> selectperm(v, 1, by=abs)
1-element Array{Int64,1}:
 1

Here, the selectperm function is used with the by=abs argument to obtain a partial permutation of the vector v where the element with the smallest absolute value is selected.

julia> v = [5, 2, 8, 3, 1];
julia> selectperm(v, 1, lt=>, by=x->-x)
1-element Array{Int64,1}:
 8

In this example, the selectperm function is used with the lt=> argument to obtain a partial permutation of the vector v where the element with the largest value is selected.

julia> v = [5, 2, 8, 3, 1];
julia> selectperm(v, 1, alg=QuickSort)
1-element Array{Int64,1}:
 1

This example showcases the usage of selectperm with the alg=QuickSort argument to obtain a partial permutation of the vector v using the QuickSort algorithm. The element with the smallest value is selected.

See Also

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