Can someone clarify why the value of a variable in my loop is not updating until the loop is closed?

Question

This is my function

def rating(array)
  sum_count = array.values.inject(0) { |sum_count,value| sum_count + value }
  run_count = 0
  array.each do |tag,count|
    run_count += count
    cum_distn = run_count/sum_count
    logger.debug "cum_distn is #{cum_distn.to_f}; run_count is #{run_count.to_f}; sum_count is #{sum_count}"
    if cum_distn < 0.25
      ...
    elsif cum_distn < 0.5
      ...
    else
      ...
    end
  end
end

For 2 objects in my array with counts of 1 each, my logger is showing this:

cum_distn is 0.0; run_count is 1.0; sum_count is 2
cum_distn is 1.0; run_count is 2.0; sum_count is 2

It seems that the value of cum_distn is only updating once one loop is complete whilst I intend for it to update immediately before the if function opens. I have two questions:

(a) Why is this happening (as I can't see any logical explanation)?

(b) How can I rectify this to do what I want?

Not yet finished reading your question but you should replace `def rating(array)` by `def rating(hash)` because `hash.values` makes more sense than `array.values`... — Damien, Dec 22 '11 at 15:56

score 3 · Accepted Answer · answered Dec 22 '11 at 15:56

3

You are using integer division, so the result of run_count / sum_count gets truncated. To fix, simply convert one of them to Float before calculating cum_distn. For example:

cum_distn = run_count.to_f / sum_count

answered Dec 22 '11 at 15:56

Paolo Capriotti

4,052
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25

Damien · Answer 2 · 2011-12-22T16:20:20.640

1) It happens because 3/2 #=> 1 but 3.0/2 # => 1.5. In other terms, integer/integer #=> integer and float/integer #=> float

2) Just call to_f one time, at the beginning (not in a loop because it's really not performant):

def rating(hash)
  sum_count = hash.values.inject(:+).to_f
  hash.inject(0) do |run_count, (tag, count)|
    run_count += count
    cum_dist = run_count/sum_count
    logger.debug "cum_distn is #{cum_distn}; run_count is #{run_count}; sum_count is #{sum_count}"
    ...
    run_count # return run_count
  end
end

Can someone clarify why the value of a variable in my loop is not updating until the loop is closed?

2 Answers2