Git : moving a remote branch

 programming  No Responses »
Dec 292009
 

One can’t actually move a remote branch, but you can copy a branch and delete a branch, so…

Copy oldbranch in repo to newbranch.

git push {repo} {oldbranch}:heads/{newbranch}

Ex: git push origin foobranch:barbranch
renames foobranch to barbranch

Remove a remote branch: it’s all about the colon:

git push <remote_repo> :heads/<branch>

Example: git push origin :heads/some-branch removes some-branch from the remote repo (apparently git push origin :some-branch works as well).

This works for removing a tag as well: git push origin :sometag

Random constrained permutations in Ruby

 ruby  No Responses »
Dec 172009
 

Look, Ma, these are my baby steps in algorithms!

# list is the elements to be permuted
# y is the number of results desired
# z is the number of elements per result
# equalizer keeps track of who got used how many times
def constrained_permutations list, y, z
  list.uniq! # Never trust the user. We want no repetitions.
  equalizer = {}
  list.each { |element| equalizer[element] = 0 }

  results = []
  # Do this until we get as many results as desired
  while results.size < y
    pool = []
    puts pool
    least_used = equalizer.each_value.min
    # Find how used the least used element was
    while pool.size < z
      # Do this until we have enough elements in this resultset
      element = nil
      while element.nil?
        # If we run out of "least used elements", then we need to increment
        # our definition of "least used" by 1 and keep going.
        element = list.shuffle.find do |x|
          !pool.include?(x) && equalizer[x] == least_used
        end
        least_used += 1 if element.nil?
      end
      equalizer[element] += 1
      # This element has now been used one more time.
      pool << element
    end
    results << pool
  end
  return results
end

constrained_permutations [0,1,2,3,4,5,6], 6, 2
=> [[4, 0], [1, 3], [2, 5], [6, 0], [2, 5], [3, 6]]
constrained_permutations [0,1,2,3,4,5,6], 6, 2
=> [[4, 5], [6, 3], [0, 2], [1, 6], [5, 4], [3, 0]]

Inter-array permutations in Ruby

 food for thought, ruby  No Responses »
Dec 172009
 

I don’t really have a better name for this. It’s also not completely clean, but it works. I had, almost a year ago (362 days ago), written a blog post about lexicographic permutations. That was about permutations of elements within one array.
Someone on ruby-forum asked about permutations between multiple arrays. I found something in C#, which I was happy to transcribe to Ruby and tweak a little.

def array_permutations array, index=0
  # index is 0 by default : start at the beginning, more elegant.
  return array[-1] if index == array.size - 1 # Return last element if at end.
  result = []
  array[index].each do |element| # For each array
    array_permutations(array, index + 1).each do |x| # Permute permute permute
      result << "#{element}, #{x}"
    end
  end
  return result
end

So, we get this:

first = ['one', 'two']
second = ['three', 'four']
third = 'five', 'six']
result = array_permutations [first, second, third]
=> ["one, three, five", "one, three, six", "one, four, five", "one, four, six", "two, three, five", "two, thre
e, six", "two, four, five", "two, four, six"]

Magic!

——
Edit – of course, my solution is hackish, and someone came up with a quicker and more elegant solution:

def fancy_array_permutation array
  return array[0] if array.size == 1
  first = array.shift
  return first.product( fancy_array_permutation(array) ).map {|x| x.flatten.join(" ")}
end

This gives the same result as above.

On re-reading old code

 ruby  No Responses »
Dec 092009
 

I came across this beauty:

def same_modality? list
  check = list[0][0]
  list.each do |i|
    return false if check != i[0]
  end
  return true
end

This was “necessary” because I got an array of one-element arrays back, and I wanted to check whether or not that one element was the same across the array.

Three seconds of thinking made me realize that just maybe, I could do this:

list.uniq.size == 1

I -like- Ruby.