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change array column values without loop - khalidreemy - May-05-2019
Hello
I need to update a column values of an array without using a loop.
Is there any way to update with criteria.
1 0.168425
2 0
3 0
4 0.752781
5 0.235684
I need to double the values below 0.5 , so the result will become like this:
1 0.33685
2 0
3 0
4 0.752781
5 0.471368
RE: change array column values without loop - scidam - May-05-2019
The answer depends on what container did you use to store the data. If you are working with numpy arrays,
you can do that as follows:
import numpy as np x = np.array([0.16, 0, 0, 0.65, 0.17]) x[x < 0.5] *= 2If your data is presented as a column of Pandas dataframe, you can do it by almost similar way:
# df Pandas data frame df[df.iloc[:, <column number>]<0.5] *= 2
RE: change array column values without loop - DeaD_EyE - May-05-2019
List Comprehension with conditional expression:
data = [0.16, 0, 0, 0.65, 0.17] result = [x * 2 if x < 0.5 else x for x in data]If you use numpy or pandas, you're using implicit for-loops. But in the numpy case, the for-loop is written in C. Operations on a numpy arrays are much faster than looping and doing the same in Python. To know how you can do broadcast operations with Python, is useful.