Array.sort problem


#1

Dear all, I’m a newbie to ruby and today when I’m writing a simple
script to process some data, I found something I can’t understand.

The data is stored in several column seperated by tab or space. I use
the following code to get the data (assuming the data comes from
standard input and all numbers are integer)

data=[]
counter = 0
while line = STDIN.gets
data[counter] = line.split
data[counter].map! {|str| str.to_i}
counter += 1
end

hence data[i] is an array hold all the numbers in the ith line, data[i]
[j] is the number on ith line and jth column. Then what I want the
script to do is sorting lines according to a specified column. I
thought the following code should work:

result = data.sort {|x, y| x[col] <=> y[col] }

where the col determine which column the script will sort according
to. However ruby raise a error saying:
"undefined method <=>' for nil:NilClass (NoMethodError) from ana.rb:16:insort’
from ana.rb:16
"

I have to write the code as

result = data.sort {|x, y| x[col].to_i <=> y[col].to_i }

to let the script run properly. I’m quite confused here. I think the
elements of array data are converted to integer when the code

data[counter].map! {|str| str.to_i}

finished. However why ruby still requires a explicit conversion when I
use the data.sort?


#2

On 4/21/07, Larme removed_email_address@domain.invalid wrote:

data[counter] = line.split

to let the script run properly. I’m quite confused here. I think the
elements of array data are converted to integer when the code

data[counter].map! {|str| str.to_i}

finished. However why ruby still requires a explicit conversion when I
use the data.sort?

Yes, they are. You might be doing some typo or other crap. Following
program runs verbatim:

data=[]
counter = 0
while line = STDIN.gets
data[counter] = line.split
data[counter].map! {|str| str.to_i}
counter += 1
end

#p data.sort_by { |x| x[2] } #=> you can use sort_by as an alternative

p data.sort {|x,y| x[2] <=> y[2] } #=> This also work.


#3

Larme wrote:

use the data.sort?
If you have an array arr with n elements which you all turn into
integers,
arr[i] with i>=n will still be nil. So if in your case not all rows have
more
than col columns, that would explain the problem.

HTH,
Sebastian H.


#4

On 21.04.2007 20:16, Larme wrote:

data[counter] = line.split

to let the script run properly. I’m quite confused here. I think the
elements of array data are converted to integer when the code

data[counter].map! {|str| str.to_i}

finished. However why ruby still requires a explicit conversion when I
use the data.sort?

You probably have lines with differing number of entries and thus
sometimes x[col] just returns nil.

You could do something like:

data.sort_by {|x| x[col].to_i}
data.sort_by {|x| x[col] || 0}

If you want to be sure that you extract only integers you could do

l.scan(/\d+/).map {|x| x.to_i}

instead of the split.

Lots of options…

Kind regards

robert


#5

On Apr 21, 2007, at 2:20 PM, Larme wrote:

1
2 data=[]
3 counter = 0
4 while line = STDIN.gets
5 data[counter] = line.split
6 data[counter].map! {|str| str.to_i}
7 counter += 1
8 end

Ok, so I’m a noob trying to learn something here…

Shouldn’t line 4 be presented with a double = (==) since you’re
trying do something while line == STDIN.gets?

Also, does STDIN.gets need to be stated in a previous line? Or will
it be prompted from within the ‘while’ statement.

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#6

On Apr 22, 3:25 am, Robert K. removed_email_address@domain.invalid wrote:

script to do is sorting lines according to a specified column. I

use the data.sort?

l.scan(/\d+/).map {|x| x.to_i}

instead of the split.

Lots of options…

Kind regards

    robert

Thank all of you. Yes, the problem is that the column number is not
fixed – it should be, but my friend who prepare the data made some
thing wrong.


#7

On Apr 21, 2007, at 8:16 PM, Philip M. Gollucci wrote:

4 while line = STDIN.gets

No, the assignment of line = STDIN.gets happens first which reads
up to a ‘\n’ including it. While then loops while this value is true.

Oh, so it’s not checking whether line == STDIN.gets (immediately),
but rather assigning STDIN.gets to line, and then checking whether
that’s true?

Nice, I learned something!

---------------------------------------------------------------|
~Ari
“I don’t suffer from insanity. I enjoy every minute of it” --1337est
man alive


#8

4 while line = STDIN.gets

Ok, so I’m a noob trying to learn something here…

Shouldn’t line 4 be presented with a double = (==) since you’re trying
do something while line == STDIN.gets?
No, the assignment of line = STDIN.gets happens first which reads up to
a ‘\n’ including it. While then loops while this value is true.

When there is no more inmput, line will be assigned nothing which is
false and the loop ends.

This works identically to other languages like perl/python/php

Philip M. Gollucci (removed_email_address@domain.invalid) 323.219.4708
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