Python error type string

Question

I have a dataframe, DF of columns of data as such:

        X       Y         Z     DIST_1
0       309000  563250    0     681483125
1       309000  563300    0     679910525
2       309000  563350    0     678342925

Upon attempting to run math.sqrt on DIST_1 with the following

DF['DIST'] = math.sqrt(DF['DIST_1'])

I am getting

TypeError: cannot convert the series to <class 'float'>

I have tried running three separate functions, on the individual column and the entire DataFrame, to fix this problem:

DF['DIST_1'] = pd.to_numeric(DF['DIST_1'])

DF['DIST_1'] = (DF['DIST_1']).astype(float)

DF= DF.applymap(float)

Each of these appears to have the desired results of changing DIST_1 to a float. Here is the output after running

DF['DIST_1'] = (DF['DIST_1']).astype(float)

        X       Y         Z     DIST_1
0       309000  563250    0     681483125.0
1       309000  563300    0     679910525.0
2       309000  563350    0     678342925.0

Again I run

DF['DIST'] = math.sqrt(DF['DIST_1'])

but the result is again

TypeError: cannot convert the series to <class 'float'>

What is the error in my code or my approach?

Did you try the map function? I think sqrt only works on a number, not a pandas series, so maybe you could do it with the map function. — user7628486
– user7628486, Commented Feb 19, 2018 at 12:46
Yes. This changes all columns to floats but I'm still getting the same error. — acolls_badger
– acolls_badger, Commented Feb 19, 2018 at 12:47

Graipher · Accepted Answer · 2018-05-22 19:03:07Z

4

The problem is that math.sqrt can only take a single number, not a pandas.Series. One way is to use apply, as @Kalyan recommended in the other answer.

The easier solution is to use a function that can handle a vector of floats, numpy.sqrt:

import numpy as np
DF['DIST'] = np.sqrt(DF['DIST_1'])

This should also be significantly faster than repeatedly applying the math.sqrt function to every element of the series.

edited May 22, 2018 at 19:03

answered Feb 19, 2018 at 12:59

Graipher

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rawwar · Accepted Answer · 2018-02-19 12:52:11Z

1

you can try the following

DF['DIST_1'] = DF['DIST_1'].apply(math.sqrt)

answered Feb 19, 2018 at 12:52

rawwar

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