Iterated sum and mean

Question

I have a data with two columns as shown below. i am trying to estimate a standard deviation of the second column for each of the values of the first column. So 284, 285 and 286 values should have their consecutive standard deviation values.

I managed to calculate the running sum, but am stuck on the mean value calculation. Here is my code so far:

b = [(line.split("\t")) for line in data]
sums = [(sum(float(v) for k, v in g)) for k, g in groupby(b, key=itemgetter(0))]

lens = [(len(float(v) for k, v in g)) for k, g in groupby(b, key=itemgetter(0))]

sums works fine and calculates the summation per each change of the first column, however len() does not work and crashes with message:

TypeError: object of type 'generator' has no len()

Has anyone faced this before?

Did you try searching *that exact error message*? – jonrsharpe Mar 14 '16 at 23:19 — jonrsharpe, Mar 14 '16 at 23:19

score 3 · Answer 1 · answered Mar 14 '16 at 23:19

3

The error is in this part of the code:

len(float(v) for k, v in g)

That is equivalent to:

len(g)

The generator the error is referring to is the list comprehension you are doing inside the brackets. If you actually wanted to perform the action you've written (and I don't think you do), the code would need to be:

len([float(v) for k, v in g])

answered Mar 14 '16 at 23:19

Alex Taylor

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It's a duplicate question, no need for an answer, since the existing ones are good already. :) – gsamaras Mar 14 '16 at 23:20

Iterated sum and mean

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