Select nested array in array from an arugment in Ruby

Question

I have an array:

foo = [[51, 05,1.0],[51,979,0.18]]

What I would like to do is take this array and select all nested arrays that have the last value less than 1. So the output from the above would be

result = [[51,979,0.18]]

I have tried:

foo.select { |p| p.last < 1 }

But I get the error:

NoMethodError (undefined method `last'

The array is much larger than just two but I have listed the above as en example. I thought .select would be right, but I can not get it to work.

this code works, so probably one element in foo may is not an array at all. — tokland
– tokland, Commented Mar 9, 2012 at 11:43
Your error message should tell what class the receiver belongs to. Does it say that what you have is an array? And are you using an old version of Ruby? — sawa
– sawa, Commented Mar 9, 2012 at 11:45

Waynn Lue · Accepted Answer · 2012-03-09 11:35:36Z

3

Your code works for me.

irb(main):007:0> foo = [[51, 05,1.0],[51,979,0.18]]
=> [[51, 5, 1.0], [51, 979, 0.18]]
irb(main):008:0> foo.select { |p| p.last < 1 }
=> [[51, 979, 0.18]]

answered Mar 9, 2012 at 11:35

Waynn Lue

11.4k8 gold badges53 silver badges77 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

jack · Accepted Answer · 2012-03-09 15:42:13Z

2

If you think bad values may exist in your data, it's worth protecting against them:

foo = [ [51, 05,1.0], [51,979,0.18], 4, nil, {:foo => :bar} ]

foo.select do |x|
    if (x.respond_to?(:last))
        x.last < 1
    else
        # the warn call evaluates to nil, thus skipping this element
        warn("#{x.class} does not respond to method last")
    end
end

answered Mar 9, 2012 at 15:42

jack

1721 silver badge12 bronze badges

Comments

Mgrandjean · Accepted Answer · 2012-03-09 11:36:49Z

1

you were so close! instead of p.last use p[-1]

so

foo.select{ |p| p[-1] < 1}

answered Mar 9, 2012 at 11:36

Mgrandjean

3171 silver badge6 bronze badges

Comments

Maksim Ravnovesov · Accepted Answer · 2012-03-09 11:40:35Z

1

what about this ?

foo.select { |p| p.at(-1) < 1 }

answered Mar 9, 2012 at 11:40

Maksim Ravnovesov

2734 silver badges12 bronze badges

2 Comments

Charlie Davies Over a year ago

can you think of any reason why i get NoMethodError (undefined method `at' for

Lee Jarvis Over a year ago

@CharlieDavies obviously because it's not an Array. You need to specify more information. undefined method 'at' for what exactly? the rest of the error message is there, please show it to us. Also, this code is no different from yours. array.at(-1) array[-1] and array.last all do the same thing

Collectives™ on Stack Overflow

Select nested array in array from an arugment in Ruby

4 Answers 4

Comments

Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related