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# Distribute items into containers in twos - Rails

clueless
1#
clueless Published in 2018-02-14 08:22:00Z
 I have a list of 10 items -- it is an array of hashes. [{ id: 1, name: 'one'}, { id: 2, name: 'two' } .. { id: 10, name: 'ten' }]  I also have a random number of containers -- let's say 3, in this case. These containers are hashes with array values. { one: [], two: [], three: [] }  What I want to do, is iterate over the containers and drop 2 items at a time resulting in: { one: [{id:1}, {id:2}, {id:7}, {id:8}], two: [{id:3}, {id:4}, {id:9}, {id:10}], three: [{id:5}, {id:6}] }  Also, if the item list is an odd number (11), the last item is still dropped into the next container. { one: [{id:1}, {id:2}, {id:7}, {id:8}], two: [{id:3}, {id:4}, {id:9}, {id:10}], three: [{id:5}, {id:6}, {id:11}] }  note: the hashes are snipped here so it's easier to read. My solution is something like this: (simplified) x = 10 containers = { one: [], two: [], three: [] } until x < 1 do containers.each do |c| c << 'x' c << 'x' end x -= 2 end puts containers  I'm trying to wrap my head around how I can achieve this but I can't seem to get it to work.
2#
 Round-robin pair distribution into three bins: bins = 3 array = 10.times.map { |i| i + 1 } # => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] array. each_slice(2). # divide into pairs group_by. # group into bins with_index { |p, i| i % bins }. # round-robin style values. # get rid of bin indices each(&:flatten!) # join pairs in each bin  Completely different approach, stuffing bins in order: base_size, bins_with_extra = (array.size / 2).divmod(bins) pos = 0 bins.times.map { |i| length = 2 * (base_size + (i < bins_with_extra ? 1 : 0)) # how much in this bin? array[pos, length].tap { pos += length } # extract and advance } # => [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10]]  If you absolutely need to have this in a hash, Hash[%i(one two three).zip(binned_array)] # => {:one=>[1, 2, 7, 8], :two=>[3, 4, 9, 10], :three=>[5, 6]}  The lovely (but likely not as performant) solution hinted at by Stefan Pochmann: bins.times.with_object(array.to_enum).map { |i, e| Array.new(2 * (base_size + (i < bins_with_extra ? 1 : 0))) { e.next } } 
 You can use Enumerable#each_slice to iterate over a range from 0 to 10 in 3s and then append to an array of arrays: containers = [ [], [], [] ] (1...10).each_slice(3) do |slice| containers[0] << slice[0] containers[1] << slice[1] containers[2] << slice[2] end p containers # [[1, 4, 7], [2, 5, 8], [3, 6, 9]] 
 This is just to show a different approach (and I would probably not use this one myself). Given an array of items and the containers hash: items = (1..10).to_a containers = { one: [], two: [], three: [] }  You could dup the array (in order not to modify the original one) and build an enumerator that cycles each_value in the hash: array = items.dup enum = containers.each_value.cycle  Using the above, you can shift 2 items off the array and push them to the next container until the array is emtpy?: enum.next.push(*array.shift(2)) until array.empty?  Result: containers #=> {:one=>[1, 2, 7, 8], :two=>[3, 4, 9, 10], :three=>[5, 6]}