I don't really understand inject

[Mike Barton]

I think these methods should both do the same thing. The second works,
however in the first I get errors that string is not matched, where
hash is an instance of String not hash

def sequences
self.alignment.split(/\n/).inject(Hash.new) do |hash, line|
id, sequence = line.split(/\s+/,2)
# hash.class == String
hash[id] = sequence
end
end

def sequences
hash = Hash.new
self.alignment.split(/\n/).each do |line|
id, sequence = line.split(/\s+/,2)
# hash.class == Hash
hash[id] = sequence
end
hash
end

 

[Rob Biedenharn]

I think these methods should both do the same thing. The second works,
however in the first I get errors that string is not matched, where
hash is an instance of String not hash

def sequences
self.alignment.split(/\n/).inject(Hash.new) do |hash, line|
id, sequence = line.split(/\s+/,2)
# hash.class == String
hash[id] = sequence

hash # value of block will be the last expression

end
end

def sequences
hash = Hash.new
self.alignment.split(/\n/).each do |line|
id, sequence = line.split(/\s+/,2)
# hash.class == Hash
hash[id] = sequence
end
hash
end

The value of the block becomes the first block parameter in the next
iteration.

-Rob

Rob Biedenharn http://agileconsultingllc.com
(e-mail address removed)

 

[Jesús Gabriel y Galán]

I think these methods should both do the same thing. The second works,
however in the first I get errors that string is not matched, where
hash is an instance of String not hash

def sequences
self.alignment.split(/\n/).inject(Hash.new) do |hash, line|
id, sequence = line.split(/\s+/,2)
# hash.class == String
hash[id] = sequence
end
end

How inject works is that it passes the block two values:
an accumulator and one of the elements in the enumerable
(one at a time). In each iteration, the accumulator will be the
return value of the block in the previous iteration.

So in your example, if you want the accumulator to be a hash,
your block should return a hash. Try this (untested):

def sequences
self.alignment.split(/\n/).inject(Hash.new) do |hash, line|
id, sequence = line.split(/\s+/,2)
# hash.class == String
hash[id] = sequence
hash # <<< the change
end
end

Hope this helps,

Jesus.

 

[Mike Barton]

I see, I see, I see.
That solved the problem. Thanks for that help injection!
Ha Ha Ha!

I think these methods should both do the same thing. The second works,
however in the first I get errors that string is not matched, where
hash is an instance of String not hash

def sequences
   self.alignment.split(/\n/).inject(Hash.new) do |hash, line|
     id, sequence = line.split(/\s+/,2)
     # hash.class == String
     hash[id] = sequence
   end
end

How inject works is that it passes the block two values:
an accumulator and one of the elements in the enumerable
(one at a time). In each iteration, the accumulator will be the
return value of the block in the previous iteration.

So in your example, if you want the accumulator to be a hash,
your block should return a hash. Try this (untested):

def sequences
    self.alignment.split(/\n/).inject(Hash.new) do |hash, line|
      id, sequence = line.split(/\s+/,2)
      # hash.class == String
      hash[id] = sequence
      hash    # <<< the change
    end
 end

Hope this helps,

Jesus.

 

[Robert Dober]

I see, I see, I see.
That solved the problem. Thanks for that help injection!
Ha Ha Ha!

Nice one, fortunately you did not ask for help on reduce (which is an
alias of inject) .
Robert