ruby hash array value changes when assigned array value changes

Question

im trying to find all possible sums using numbers from the testArray. i am assigning arrays to a hash, it uses sum as key and stores the integers from testArray that add up to the sum:

testArray=[1,2,3,4] @possibleSums=Hash.new {|h,k| h[k] = [] } for j in 0..testArray.size-1 tmpSum=0 output="" @sumArray=[] for k in j..testArray.size-1 tmpSum=tmpSum+testArray[k] output=output+"+"+testArray[k].to_s @sumArray.push(testArray[k]) @possibleSums[tmpSum]=@sumArray p output+"="+tmpSum.to_s end end

the problem is that i noticed that as @sumArray changes through every iteration of the loop, the previous recorded hash key value also changes. what am i doing wrong?

example:

output: "+1=1" @sumArray: [1] @possibleSums: {1=>[1]} output: "+1+2=3" @sumArray: [1, 2] @possibleSums: {1=>[1, 2], 3=>[1, 2]} output: "+1+2+3=6" @sumArray: [1, 2, 3] @possibleSums: {1=>[1, 2, 3], 3=>[1, 2, 3], 6=>[1, 2, 3]}

you can see that value of key 1 and 3 kept changing with @sumArray

red_menace is right .. you can use @possibleSums[tmpSum][email protected] instead — max pleaner
– max pleaner, Commented Sep 12, 2021 at 18:12
A more Ruby-like way to obtain an array of all sums for test_array=[1,3,7,10] is as follows: require 'set'; (1..test_array.size).each_with_object(Set.new) { |n,st| test_array.combination(n).each { |a| st << a.sum } }.to_a #=> [1, 3, 7, 10, 4, 8, 11, 13, 17, 14, 18, 20, 21]. I wrote test_array rather than testArray because, by convention, Ruby uses snake case for names of variables and methods. — Cary Swoveland
– Cary Swoveland, Commented Sep 12, 2021 at 19:58
so @possibleSums[tmpSum][email protected] is the proper way to assign instance of an array to a hash? — gkeepa
– gkeepa, Commented Sep 12, 2021 at 22:16

gkeepa · Accepted Answer · 2021-09-16 01:59:59Z

You are putting a reference to @sumArray in the hash. – red_menace Sep 12 at 17:48

red_menace is right .. you can use @possibleSums[tmpSum][email protected] instead

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