How Yield statement in ruby works?

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Can someone please show how to correctly format this yield statement, and why my methodology for this yield statement is incorrect? When run, the compiler results in an "undefined method 'length' error. "Test" is the main class.

  def bubble_sort_by(array)

    len = array.length - 1

    while len > 0

      for i in(1..len)

        @left = array[i]

        @right = array[i - 1]

        yield

        if @left - @right > 0

           array[i - 1], array[i] = array[i], array[i - 1]

        end

      end

      len -= 1

    end

   p array

end



  Test.bubble_sort_by(%w[hi hello hey]) do |left, right|

    left.length - right.length

  end

edited Nov 25 '18 at 10:19

DonPaulie

919924

asked Nov 25 '18 at 0:26

Lawleyenda

359

If the block were { |a,b| a*b } and c = yield(2,3), a and b would be assigned values 2 and 3, respectively, so the block would return 6, which would be assigned to the variable c.

– Cary Swoveland
Nov 25 '18 at 0:34

Thank you for responding, Cary. @CarySwoveland how is " if yield(array[i-1], array[i]) > 1" not the same as the code written above for the if statement.

– Lawleyenda
Nov 25 '18 at 0:46

No, the body of the block (left.length - right.length) only has access to the variables directly passed to it by yield, not to any variables or methods that would be accessible within the method doing the yielding (bubble_sort_by).

– Max
Nov 25 '18 at 2:13

add a comment |

  def bubble_sort_by(array)

    len = array.length - 1

    while len > 0

      for i in(1..len)

        @left = array[i]

        @right = array[i - 1]

        yield

        if @left - @right > 0

           array[i - 1], array[i] = array[i], array[i - 1]

        end

      end

      len -= 1

    end

   p array

end



  Test.bubble_sort_by(%w[hi hello hey]) do |left, right|

    left.length - right.length

  end

edited Nov 25 '18 at 10:19

DonPaulie

919924

asked Nov 25 '18 at 0:26

Lawleyenda

359

If the block were { |a,b| a*b } and c = yield(2,3), a and b would be assigned values 2 and 3, respectively, so the block would return 6, which would be assigned to the variable c.

– Cary Swoveland
Nov 25 '18 at 0:34

Thank you for responding, Cary. @CarySwoveland how is " if yield(array[i-1], array[i]) > 1" not the same as the code written above for the if statement.

– Lawleyenda
Nov 25 '18 at 0:46

No, the body of the block (left.length - right.length) only has access to the variables directly passed to it by yield, not to any variables or methods that would be accessible within the method doing the yielding (bubble_sort_by).

– Max
Nov 25 '18 at 2:13

add a comment |

  def bubble_sort_by(array)

    len = array.length - 1

    while len > 0

      for i in(1..len)

        @left = array[i]

        @right = array[i - 1]

        yield

        if @left - @right > 0

           array[i - 1], array[i] = array[i], array[i - 1]

        end

      end

      len -= 1

    end

   p array

end



  Test.bubble_sort_by(%w[hi hello hey]) do |left, right|

    left.length - right.length

  end

edited Nov 25 '18 at 10:19

DonPaulie

919924

asked Nov 25 '18 at 0:26

Lawleyenda

359

  def bubble_sort_by(array)

    len = array.length - 1

    while len > 0

      for i in(1..len)

        @left = array[i]

        @right = array[i - 1]

        yield

        if @left - @right > 0

           array[i - 1], array[i] = array[i], array[i - 1]

        end

      end

      len -= 1

    end

   p array

end



  Test.bubble_sort_by(%w[hi hello hey]) do |left, right|

    left.length - right.length

  end

ruby-on-rails ruby yield

edited Nov 25 '18 at 10:19

DonPaulie

919924

asked Nov 25 '18 at 0:26

Lawleyenda

359

edited Nov 25 '18 at 10:19

DonPaulie

919924

asked Nov 25 '18 at 0:26

Lawleyenda

359

edited Nov 25 '18 at 10:19

DonPaulie

919924

edited Nov 25 '18 at 10:19

DonPaulie

919924

edited Nov 25 '18 at 10:19

DonPaulie

919924

asked Nov 25 '18 at 0:26

Lawleyenda

359

asked Nov 25 '18 at 0:26

Lawleyenda

359

asked Nov 25 '18 at 0:26

Lawleyenda

359

If the block were { |a,b| a*b } and c = yield(2,3), a and b would be assigned values 2 and 3, respectively, so the block would return 6, which would be assigned to the variable c.

– Cary Swoveland
Nov 25 '18 at 0:34

Thank you for responding, Cary. @CarySwoveland how is " if yield(array[i-1], array[i]) > 1" not the same as the code written above for the if statement.

– Lawleyenda
Nov 25 '18 at 0:46

No, the body of the block (left.length - right.length) only has access to the variables directly passed to it by yield, not to any variables or methods that would be accessible within the method doing the yielding (bubble_sort_by).

– Max
Nov 25 '18 at 2:13

add a comment |

If the block were { |a,b| a*b } and c = yield(2,3), a and b would be assigned values 2 and 3, respectively, so the block would return 6, which would be assigned to the variable c.

– Cary Swoveland
Nov 25 '18 at 0:34

Thank you for responding, Cary. @CarySwoveland how is " if yield(array[i-1], array[i]) > 1" not the same as the code written above for the if statement.

– Lawleyenda
Nov 25 '18 at 0:46

No, the body of the block (left.length - right.length) only has access to the variables directly passed to it by yield, not to any variables or methods that would be accessible within the method doing the yielding (bubble_sort_by).

– Max
Nov 25 '18 at 2:13

If the block were { |a,b| a*b } and c = yield(2,3), a and b would be assigned values 2 and 3, respectively, so the block would return 6, which would be assigned to the variable c.

– Cary Swoveland
Nov 25 '18 at 0:34

Thank you for responding, Cary. @CarySwoveland how is " if yield(array[i-1], array[i]) > 1" not the same as the code written above for the if statement.

– Lawleyenda
Nov 25 '18 at 0:46

No, the body of the block (left.length - right.length) only has access to the variables directly passed to it by yield, not to any variables or methods that would be accessible within the method doing the yielding (bubble_sort_by).

– Max
Nov 25 '18 at 2:13

add a comment |

2 Answers
2

active

oldest

votes

because you need to pass arguments to yield.

try to change the line with yield into:
compared = yield @left, @right
and deal with the compared result

answered Nov 25 '18 at 1:05

DonPaulie

919924

add a comment |

As I said in my comment on the question, yield needs to pass values for the block variables. Your code therefore needs to be modified as follows.

def bubble_sort_by(array)

    len = array.length - 1

    while len > 0

      for i in(1..len)

        @left = array[i]

        @right = array[i - 1]

        if yield(@left, @right) > 0

          array[i - 1], array[i] = array[i], array[i - 1]

        end

      end

      len -= 1

    end

  array

end



bubble_sort_by(%w[hi hello hey]) do |left, right|

  left.length - right.length

end

  #=> ["hello", "hey", "hi"]

If, as here, the block being yielded to has block variables, the values of those variables must be passed as yield's arguments. The value computed by the block is then returned as though yield were the invocation of a method.

If you prefer, you could replace the first line with

def bubble_sort_by(array, &block)

and replace if yield(@left, @right) > 0 with

if block.call(@left, @right) > 0

Here & converts the bloc to a Proc which is held by the variable block.

edited Nov 25 '18 at 18:42

answered Nov 25 '18 at 1:52

Cary Swoveland

71.5k54167

One small suggestion: would be nice to also explain what you changed and why is needed.

– Rada Bogdan
Nov 25 '18 at 8:20

@Rada, that's a good point. The only reason I didn't elaborate was because I had eariler left an abbreviated explanation in a comment on the question. But you are right; I'll edit my answer.

– Cary Swoveland
Nov 25 '18 at 8:24

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

because you need to pass arguments to yield.

try to change the line with yield into:
compared = yield @left, @right
and deal with the compared result

answered Nov 25 '18 at 1:05

DonPaulie

919924

add a comment |

because you need to pass arguments to yield.

try to change the line with yield into:
compared = yield @left, @right
and deal with the compared result

answered Nov 25 '18 at 1:05

DonPaulie

919924

add a comment |

because you need to pass arguments to yield.

try to change the line with yield into:
compared = yield @left, @right
and deal with the compared result

answered Nov 25 '18 at 1:05

DonPaulie

919924

because you need to pass arguments to yield.

try to change the line with yield into:
compared = yield @left, @right
and deal with the compared result

answered Nov 25 '18 at 1:05

DonPaulie

919924

answered Nov 25 '18 at 1:05

DonPaulie

919924

answered Nov 25 '18 at 1:05

DonPaulie

919924

answered Nov 25 '18 at 1:05

DonPaulie

919924

add a comment |

As I said in my comment on the question, yield needs to pass values for the block variables. Your code therefore needs to be modified as follows.

def bubble_sort_by(array)

    len = array.length - 1

    while len > 0

      for i in(1..len)

        @left = array[i]

        @right = array[i - 1]

        if yield(@left, @right) > 0

          array[i - 1], array[i] = array[i], array[i - 1]

        end

      end

      len -= 1

    end

  array

end



bubble_sort_by(%w[hi hello hey]) do |left, right|

  left.length - right.length

end

  #=> ["hello", "hey", "hi"]

If you prefer, you could replace the first line with

def bubble_sort_by(array, &block)

and replace if yield(@left, @right) > 0 with

if block.call(@left, @right) > 0

Here & converts the bloc to a Proc which is held by the variable block.

edited Nov 25 '18 at 18:42

answered Nov 25 '18 at 1:52

Cary Swoveland

71.5k54167

One small suggestion: would be nice to also explain what you changed and why is needed.

– Rada Bogdan
Nov 25 '18 at 8:20

@Rada, that's a good point. The only reason I didn't elaborate was because I had eariler left an abbreviated explanation in a comment on the question. But you are right; I'll edit my answer.

– Cary Swoveland
Nov 25 '18 at 8:24

add a comment |

As I said in my comment on the question, yield needs to pass values for the block variables. Your code therefore needs to be modified as follows.

def bubble_sort_by(array)

    len = array.length - 1

    while len > 0

      for i in(1..len)

        @left = array[i]

        @right = array[i - 1]

        if yield(@left, @right) > 0

          array[i - 1], array[i] = array[i], array[i - 1]

        end

      end

      len -= 1

    end

  array

end



bubble_sort_by(%w[hi hello hey]) do |left, right|

  left.length - right.length

end

  #=> ["hello", "hey", "hi"]

If you prefer, you could replace the first line with

def bubble_sort_by(array, &block)

and replace if yield(@left, @right) > 0 with

if block.call(@left, @right) > 0

Here & converts the bloc to a Proc which is held by the variable block.

edited Nov 25 '18 at 18:42

answered Nov 25 '18 at 1:52

Cary Swoveland

71.5k54167

One small suggestion: would be nice to also explain what you changed and why is needed.

– Rada Bogdan
Nov 25 '18 at 8:20

@Rada, that's a good point. The only reason I didn't elaborate was because I had eariler left an abbreviated explanation in a comment on the question. But you are right; I'll edit my answer.

– Cary Swoveland
Nov 25 '18 at 8:24

add a comment |

As I said in my comment on the question, yield needs to pass values for the block variables. Your code therefore needs to be modified as follows.

def bubble_sort_by(array)

    len = array.length - 1

    while len > 0

      for i in(1..len)

        @left = array[i]

        @right = array[i - 1]

        if yield(@left, @right) > 0

          array[i - 1], array[i] = array[i], array[i - 1]

        end

      end

      len -= 1

    end

  array

end



bubble_sort_by(%w[hi hello hey]) do |left, right|

  left.length - right.length

end

  #=> ["hello", "hey", "hi"]

If you prefer, you could replace the first line with

def bubble_sort_by(array, &block)

and replace if yield(@left, @right) > 0 with

if block.call(@left, @right) > 0

Here & converts the bloc to a Proc which is held by the variable block.

edited Nov 25 '18 at 18:42

answered Nov 25 '18 at 1:52

Cary Swoveland

71.5k54167

As I said in my comment on the question, yield needs to pass values for the block variables. Your code therefore needs to be modified as follows.

def bubble_sort_by(array)

    len = array.length - 1

    while len > 0

      for i in(1..len)

        @left = array[i]

        @right = array[i - 1]

        if yield(@left, @right) > 0

          array[i - 1], array[i] = array[i], array[i - 1]

        end

      end

      len -= 1

    end

  array

end



bubble_sort_by(%w[hi hello hey]) do |left, right|

  left.length - right.length

end

  #=> ["hello", "hey", "hi"]

If you prefer, you could replace the first line with

def bubble_sort_by(array, &block)

and replace if yield(@left, @right) > 0 with

if block.call(@left, @right) > 0

Here & converts the bloc to a Proc which is held by the variable block.

edited Nov 25 '18 at 18:42

answered Nov 25 '18 at 1:52

Cary Swoveland

71.5k54167

edited Nov 25 '18 at 18:42

answered Nov 25 '18 at 1:52

Cary Swoveland

71.5k54167

answered Nov 25 '18 at 1:52

Cary Swoveland

71.5k54167

answered Nov 25 '18 at 1:52

Cary Swoveland

71.5k54167

One small suggestion: would be nice to also explain what you changed and why is needed.

– Rada Bogdan
Nov 25 '18 at 8:20

@Rada, that's a good point. The only reason I didn't elaborate was because I had eariler left an abbreviated explanation in a comment on the question. But you are right; I'll edit my answer.

– Cary Swoveland
Nov 25 '18 at 8:24

add a comment |

One small suggestion: would be nice to also explain what you changed and why is needed.

– Rada Bogdan
Nov 25 '18 at 8:20

@Rada, that's a good point. The only reason I didn't elaborate was because I had eariler left an abbreviated explanation in a comment on the question. But you are right; I'll edit my answer.

– Cary Swoveland
Nov 25 '18 at 8:24

One small suggestion: would be nice to also explain what you changed and why is needed.

– Rada Bogdan
Nov 25 '18 at 8:20

@Rada, that's a good point. The only reason I didn't elaborate was because I had eariler left an abbreviated explanation in a comment on the question. But you are right; I'll edit my answer.

– Cary Swoveland
Nov 25 '18 at 8:24

add a comment |

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