Algorithm to get group index of item in chunked array -

so have arbitrary array of items:

array = [0,1,2,3,4]; 

and when it's been chunked looks like:

array.chunk(2) =>  [[0,1],[2,3],[4]];  array.chunk(3) =>  [[0,1,2],[3,4]]; 

what i'd algorithm index of group index in, based on group size.

for instance, running algorithm on each element in array yield:

array.chunkindex( chunksize = 2, index = n )  0 => 0 1 => 0 2 => 1 3 => 1 4 => 2  array.chunkindex( chunksize = 3, index = n )  0 => 0 1 => 0 2 => 0 3 => 1 4 => 1 

so running algorithm on index chunksize = 1 yield original index.

how go doing this? clear, don't want chunk array, determine group in, without looping , without built-in functions, if possible.

also in psuedo-code:

chunkindex = index / chunksize 

it's simple integer division means case have careful of languages return float/decimal/real. cases, need floor function find integer part of result. may wish handle negative values also.