On Mon, 19 Jul 2010 04:18:48 -0700, dhruvbird wrote:
> Hello,
> I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would
> like to compute the cumulative sum of all the integers
> from index zero into another array. So for the array above, I should
> get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ]
[pedant]
The above are *lists*, not arrays. Python has arrays, but you have to
call "import array" to get them.
[/pedant]
> What is the best way (or pythonic way) to get this.
Others have given you a plethora of advanced, complicated and obscure
ways to solve this question, but I haven't seen anyone give the simplest
method (simple as in no tricks or advanced features):
data = [0, 1, 2, 1, 1, 0, 0, 2, 3]
csums = []
for x in data:
if csums:
y = x + csums[-1]
else:
y = x
csums.append(y)
We can save some code with the ternary operator:
data = [0, 1, 2, 1, 1, 0, 0, 2, 3]
csums = []
for x in data:
csums.append((x + csums[-1]) if csums else x)
Here's a version that writes the cumulative sum in place:
data = [0, 1, 2, 1, 1, 0, 0, 2, 3]
for i in range(1, len(data)):
data[i] += data[i-1]
--
Steven
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