class Array
# insert i between each element in the array
# this is O( 2n ) ( I think! Is it? ) as the length of the list is not needed, but we need to initially make a copy of the list
def intersperse( v )
tail = [ ].replace self # we need a shallow copy
first_elem = tail.first
second_elem = tail[ 1 ]
arr = [ ]
while first_elem
arr.push first_elem
if second_elem
arr.push v
tail = tail.drop 1
first_elem = tail.first
second_elem = tail[ 1 ]
else
break
end
end
arr
end
# this is faster, but I worry that for large arrays, storing i in memory will makes this slower
# Bearing that in mind, since the speed at which this goes is determined by the length of the list as well as the length of the list stored in memory ( i ) is O( n^2 ) ( again, please correct me )
def intersperse( v )
arr = [ ]
i = 0
j = 0
inc_jay = lambda { j = j + 1 }
while i < length
arr[ j ] = self[ i ]
inc_jay.call
if self[ i + 1 ]
arr[ j ] = v
inc_jay.call
end
i = i + 1
end
arr
end
end
Refactorings
No refactoring yet !
Adam
June 10, 2009, June 10, 2009 15:37, permalink
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Twice the speed of your second method on my hardware, and easier on the eyes to boot. :)
class Array
def intersperse(object)
map { |element| [ element, object ] }.flatten[0..-2]
end
end
Martin Plöger
June 21, 2009, June 21, 2009 08:33, permalink
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You could also use the alias of map: collect. Depending on your task it might read better. And you could use an exclusive Range at the end (...) instead of (..) to get rid to the superfluous last object.
class Array
def intersperse(object)
collect { |element| [ element, object ] }.flatten[0...-1]
end
end
Martin Plöger
June 21, 2009, June 21, 2009 17:43, permalink
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This works too, but I don't like it better than the previous solution...
class Array
def intersperse object
zip(Array.new(length, object)).flatten[0...-1]
end
end
reima
June 25, 2009, June 25, 2009 22:45, permalink
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Your usage of flatten produces wrong results when multi-dimensional arrays are involved. E.g. try [[1,2],3].intersperse([4,5]). I would've done it this way:
class Array
def intersperse(object)
result = []
for i in 0...self.size
result << self[i]
result << object
end
result.pop
result
end
end
Intersperse is a method of the array class
Intersperse takes an object o, and returns the array ( self ), with o inserted between each element of self.