Sorting a Ruby array

Question

I am trying to sort large inputs in the fastest way in ascending order. The code is something like this:

t=gets
ti=t.to_i
r=[]
for i in(0..ti)
    k=gets
    r[i]=k.to_i
end
r.sort_by{|x| -x.last}

This is giving me an error saying undefined method 'last' for nil:nilclass <nomethoderror> from tsort.rb: in sort_by from tsort.rb in 'each' from tsort.rb in 'sort_by'

I don't know where am I wrong.

That's what I have tried for sorting an array...which is r[] which has all the numbers in t! Can anyone please help.

My inputs are less than 10^6!

Try to give you're variable names more meaning. Its a bit difficult to read. — MrHus
– MrHus, Commented May 28, 2009 at 13:39
Apparently some of your Array elements are nil. That is strange, because you explicitly call to_i on all arguments. Even nil.to_i is 0. Can you let us know which input you are supplying? Is this exactly identical to your production code? — molf
– molf, Commented May 28, 2009 at 13:56

molf · Accepted Answer · 2009-05-28 13:45:40Z

4

I can't reproduce your exact error, I get undefined method 'last' for n:Fixnum (NoMethodError). That makes sense, because you're calling the last method on x, which will hold the values of your Array r, all Fixnums, which do not have a last method.

It should work if you replace the last line with:

r.sort

The sort method will sort your Array in ascending order by default.

answered May 28, 2009 at 13:45

molf

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Rômulo Ceccon · Accepted Answer · 2009-05-28 15:51:09Z

3

If you want to sort a list of integers taken from STDIN I suggest something like the following:

lines = STDIN.readlines.map { |x| x.strip.to_i }.sort
puts lines.join(', ')

It's cleaner, more rubyish and faster (read the documentation for Enumerable.sort_by to see why sort is a better alternative to sort_by).

I also see your code expects a number that says how many lines to read. You can get the same behavior by modifying the example above as follows:

line_count = gets.strip.to_i
lines = (1..line_count).collect { gets.strip.to_i }.sort
puts lines.join(', ')

edited May 28, 2009 at 15:51

answered May 28, 2009 at 13:57

Rômulo Ceccon

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2 Comments

Hick Over a year ago

i want to sort a particular quantity of numbers , that i will take as input so how to do t using lines = STDIN.readlines.map { |x| x.strip.to_i }.sort puts lines.join(', ')

Rômulo Ceccon Over a year ago

@mekasperasky: I've edited my answer to reflect your requirement.

MrHus · Accepted Answer · 2009-05-28 13:41:06Z

0

Try the sort function on Array's think it does what you need.

answered May 28, 2009 at 13:41

MrHus

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