printing 2 dimensionl hash problem

[Krekna Mektek]

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

 

[benjohn]

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).

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.

 

[Krekna Mektek]

From: Krekna Mektek [mailto:[email protected]] :
#----------------------------------------------------------
# @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 p=

rints 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 t=

he 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 =3D> nil


Krekna

eg,


C:\temp\rubygems-0.9.1>cat test.rb

h =3D {"A" =3D> [1,2,3], "B" =3D>[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

 

[Krekna Mektek]

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

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).

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.