Forgive me if this is an elementary question and I am missing something
obvious, but there is a behavior in Ruby that puzzles me a lot.
I don’t see why the two blocks below do not produce the same output.
One displays the numerically sorted array and the other does not.
Block 1
myarray = [“210”, “22”]
myarray = myarray.sort do |a,b|
a.to_i <=> b.to_i
end
puts myarray
Block 2
myarray = [“210”, “22”]
puts myarray.sort do |a,b|
a.to_i <=> b.to_i
end
In one case, I reassign myarray to the return value of the sort method
for myarray and then print myarray. In the other case, I just directly
print the return value of the sort method. Shouldn’t the return value
be the same in both cases, and therefore the output also the same?
Here is the same thing in the irb interface:
irb(main):001:0> myarray = [“210”, “22”]
=> [“210”, “22”]
irb(main):002:0> myarray = myarray.sort do |a,b|
irb(main):003:1* a.to_i <=> b.to_i
irb(main):004:1> end
=> [“22”, “210”]
irb(main):005:0> puts myarray
22
210
=> nil
irb(main):006:0> myarray = [“210”, “22”]
=> [“210”, “22”]
irb(main):007:0> puts myarray.sort do |a,b|
irb(main):008:1* a.to_i <=> b.to_i
irb(main):009:1> end
210
22
=> nil
steven
On Sat, Dec 5, 2009 at 5:14 PM, Steven Arnold
[email protected] wrote:
Block 2
myarray = [“210”, “22”]
puts myarray.sort do |a,b|
a.to_i <=> b.to_i
end
In one case, I reassign myarray to the return value of the sort method for myarray and then print myarray. In the other case, I just directly print the return value of the sort method. Shouldn’t the return value be the same in both cases, and therefore the output also the same?
Precedence.
Note that “puts myarray” returns myarray. There’s an ambiguity in
your code that’s being resolved dur to precedence. Look at the
following:
(puts myarray).sort do …
puts (myarray.sort do … )
You’re expecting the second, but you’re getting the first.
However, puts myarray.sort { … will work the way you want, because {
has higher precedence than do.
irb(main):005:0> puts myarray
=> nil
steven
–
Paul S.
http://www.nomadicfun.co.uk
[email protected]
On Sat, Dec 5, 2009 at 6:43 PM, Paul S. [email protected]
wrote:
end
Precedence.
Note that “puts myarray” returns myarray.
This is not correct. puts returns nil:
irb(main):004:0> myarray = [“210”, “22”]
=> [“210”, “22”]
irb(main):005:0> puts myarray
210
22
=> nil
There’s an ambiguity in
your code that’s being resolved dur to precedence. Look at the
following:
(puts myarray).sort do …
puts (myarray.sort do … )
You’re expecting the second, but you’re getting the first.
This is not correct. What you are getting is:
puts (myarray.sort) do …
and you are outputting the array in alphanumerical order of its string
contents.
The block is passed to the puts method, and silently ignored.
However, puts myarray.sort { … will work the way you want, because {
has higher precedence than do.
This works too if you want to keep the do…end:
irb(main):010:0> puts(myarray.sort do |a,b|
irb(main):011:2* a.to_i <=> b.to_i
irb(main):012:2> end)
22
210
=> nil
Jesus.
2009/12/5 Jesús Gabriel y Galán [email protected]:
a.to_i <=> b.to_i
Precedence.
Note that “puts myarray” returns myarray.
This is not correct. puts returns nil:
I’m so sorry. I knew something was wrong with my explanation but
posted it anyway, which was silly.
Of course puts returns nil, it says so every time I type it into irb 
–
Paul S.
http://www.nomadicfun.co.uk
[email protected]