# Printing 2 dimensionl hash problem **URL:** \ **Category:** Ruby\ **Created:** [January 18, 2007, 8:47am UTC](https://www.ruby-forum.com/t/printing-2-dimensionl-hash-problem/82211 "2007-01-18T08:47:41Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Krekna\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@Krekna\_M](https://www.ruby-forum.com/u/Krekna_M)\ **Post date:** [January 18, 2007, 8:47am UTC](https://www.ruby-forum.com/t/printing-2-dimensionl-hash-problem/82211/1 "2007-01-18T08:47:41Z")
Hi, busy with my script, I am trying to print my hash, which is built up as follows: hash: key = A, value = [1,2,3] key = B, value = [4,5,6] etc. I try this: @h.each do |key,value| print key, " is ", value.each {|x| print x, " – " }, “\n” The print is strange, becuase it looks like this now: 1 – 2 – 3 – A is 123 4 – 5 – 6 – B is 456 I don’t understand why. If I interpreted this correctly, I’ve got the following two questions: 1. How come the code block is executed first 2. After that the key and value is printed, however, I don’t see the print for the values here (except for the print in de the code block, which was executed already). Krekna ---
**Author:** ![Krekna\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@Krekna\_M](https://www.ruby-forum.com/u/Krekna_M)\ **Post date:** [January 18, 2007, 9:24am UTC](https://www.ruby-forum.com/t/printing-2-dimensionl-hash-problem/82211/2 "2007-01-18T09:24:43Z")
From: Krekna M. [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)] : #---------------------------------------------------------- # @h.each do |key,value| # print key, " is ", value.each {|x| print x, " – " }, “\n” # # The print is strange, becuase it looks like this now: # # 1 – 2 – 3 – A is 123 # 4 – 5 – 6 – B is 456 # # 1. How come the code block is executed first #---------------------------------------------------------- print expects to print a value of the expression (of course). so before prints does the writing, it has to get the value first. #---------------------------------------------------------- # 2. After that the key and value is printed, however, I don’t see the print for the values here (except for the print in de the code block, which was executed already). #---------------------------------------------------------- "value.each {…} " is an expression that returns a value, in this case the array “value”. that expression however will perform \*first a {|x| print x, “—”} for every element x in array “value”. eg, C:\temp\rubygems-0.9.1\>cat test.rb h = {“A” =\> [1,2,3], “B” =\>[4,5,6]} puts “sample 1” h.each do |key,value| print key, " is " value.each {|x| print x, " – " } print “\n” end puts puts “sample 2” h.each do |key,value| puts “#{key} is #{value.join(’ – ')}” end C:\temp\rubygems-0.9.1\>ruby test.rb sample 1 A is 1 – 2 – 3 – B is 4 – 5 – 6 – sample 2 A is 1 – 2 – 3 B is 4 – 5 – 6 hth. kind regards -botp ---
**Author:** ![Krekna\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@Krekna\_M](https://www.ruby-forum.com/u/Krekna_M)\ **Post date:** [January 18, 2007, 11:50am UTC](https://www.ruby-forum.com/t/printing-2-dimensionl-hash-problem/82211/3 "2007-01-18T11:50:22Z")
2007/1/18, Peña, Botp [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > # 1. How come the code block is executed first > > #---------------------------------------------------------- > > print expects to print a value of the expression (of course). so before prints does the writing, it has to get the value first. > #---------------------------------------------------------- > > # 2. After that the key and value is printed, however, I don’t see the > > print for the values here (except for the print in de the code block, > which was executed already). > #---------------------------------------------------------- > > "value.each {…} " is an expression that returns a value, in this case the array “value”. that expression however will perform \*first a {|x| print x, “—”} for every element x in array “value”. Thank you for your explanation! I see now, that value.each is an argument to the print, which is not what I need indeed, because like you said value.each with its code block is already printing the values, so that’s why they are printed twice. So, I’ve put the value.each on a separate line like in your example now. Thus, the value.each expression is returned first, apparently the arguments are parse before the (first) print is executed. Same as this: irb(main):012:0\> print “I”, " am ", "#{print "first “}” first I am =\> nil Krekna ---
**Author:** ![Krekna\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@Krekna\_M](https://www.ruby-forum.com/u/Krekna_M)\ **Post date:** [January 18, 2007, 10:00am UTC](https://www.ruby-forum.com/t/printing-2-dimensionl-hash-problem/82211/4 "2007-01-18T10:00:50Z")
> etc. > > I don’t understand why. If I interpreted this correctly, I’ve got the > following two questions: > > 1. How come the code block is executed first > 2. After that the key and value is printed, however, I don’t see the > print for the values here (except for the print in de the code block, > which was executed already). 🙂 I think what you want to actually do is: @h.each do |key,value| print key, " is ", value.join(’ – '), “\n” end or @h.each do |key,value| puts key, " is ", value.join(’ – ') end To hopefully answer your questions: You have asked Ruby to print out the return value of value.each{…}, which is simply value: [1,2,3] == [1,2,3].each {|n| do\_something\_with\_n\_if\_you\_like(n)} So that explains the 123 at the end of the line, because [1,2,3].to\_s is “123” Why the “1 – 2 – 3” before everything else though? Well, _before_ Ruby can execute that first “print”, it must _first_ evaluate what is being printed, just as if you had writen “print 1+2+3”. In calculating that, Ruby calls values.each {…}, and this prints out the “1 – 2 – 3” at the start of the line. Hope that helps. ---
**Author:** ![Krekna\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@Krekna\_M](https://www.ruby-forum.com/u/Krekna_M)\ **Post date:** [January 18, 2007, 11:53am UTC](https://www.ruby-forum.com/t/printing-2-dimensionl-hash-problem/82211/5 "2007-01-18T11:53:22Z")
Thank you very much, my answer was posted before I read this. I think it’s clear to me now. That’s the best way, learning by doing and talking about it what actually happens when something went wrong. Thank you too. Krekna 2007/1/18, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):