CODEWITHSUNDEEP
pythonpandasapplyjupyter-notebook
ydopico
ydopico

Reputation: 13

groupby apply not giving expected result

I am new to python, and I am trying to find the std of a circular data (wind directions) grouping the data by some characteristics. Here is a set of the df I am using.

  Profile   bin     inflow_direction
0   1        51     331.7
1   1        51     332.8
2   1        51     334.1
3   1        51     335.4
4   1        51     336.4
5   1        66     337.3
6   1        66     337.5
7   1        66     337.6
8   1        66     337.7
9   1        66     337.6

I need the std for every group of bin inside each Profile. I have defined the std function as:

def circstd(j) : samples = np.radians (j) return scipy.stats.circstd(samples, high=6.283185307179586, low=0, axis=None)

when I group:

df.groupby(['Profile','bin']).apply(circstd)

The out is: 

idscng_f  bin
 1         51     0.567811

           66     0.671470

But I was expecting

idscng_f  bin
 1         51     0.0296

           66     0.0025

What is the problem here?

Upvotes: 1

Views: 96

Answers (2)

Nickil Maveli
Nickil Maveli

Reputation: 29719

Use np.std after converting angles from degrees to radians:

def simple_circstd(j) :
    return np.std(np.radians(j))['inflow_direction']

Perform Groupby:

df.groupby(['Profile','bin']).apply(simple_circtd)

Resulting output obtained:

Profile  bin
1        51     0.029650
         66     0.002367
dtype: float64

Upvotes: 1

Ayush Kumar Singh
Ayush Kumar Singh

Reputation: 65

You can specify the SeriesGroupBy object to use apply() on.

df.groupby(['Profile','bin'])["inflow_direction"].apply(circstd) will do the work.

output:

Profile  bin
1        51     0.029650
         66     0.002367
Name: inflow_direction, dtype: float64

Upvotes: 1

Related Questions