Calculate Standard Deviation on a List of List that includes strings on some columns-CodePudding

I am trying to get the standard deviation of a lists of lists but not on all 'columns' of the list since some are numbers (middle columns). So I would skip those.

param_data = [["a", 2, 3, 6, 7, "b"],
              ["c", 6, 7, 8, 2, "d"],
              ["e", 5, 6, 8, 1, "f"]]

Expected results is:

params = [std.dev(2, 6, 5),
          std.dev(3, 7, 6),
          std.dev(6, 8, 8),
          std.dev(7, 2, 1)]

Note: not evaluating the standard deviation because it is not relevant to the question, just expressed that would be evaluated. I tried using zip(*param_data) but cannot figure out how to only zip columns 1-4.

CodePudding user response：

Use a list comprehension to get the corresponding elements, and then use zip.

from statistics import stdev

param_data = [["a", 2, 3, 6, 7, "b"],["c", 6, 7, 8, 2, "d"], ["e", 5, 6, 8, 1, "f"]]

elements = [x[1:5] for x in param_data]
print([stdev(x) for x in zip(*elements)])

This assumes that the numbers are always in that 1:5 slice; if that's not the case, we'll need more information.

CodePudding user response：

You can use list(zip(*param_data)) to transpose and isinstance to check the types, this works wherever the string columns are, even in the middle or if you have more of them:

from statistics import stdev

param_data = [["a", 2, 3, 6, 7, "b"],["c", 6, 7, 8, 2, "d"], ["e", 5, 6, 8, 1, "f"]]

cols = list(zip(*param_data))

params = [stdev(xs) for xs in cols if isinstance(xs[0], (int, float))]

print(params)

Output:

[2.0816659994661326, 2.0816659994661326, 1.1547005383792515, 3.2145502536643185]