Change the pandas.series elements using apply and transform

Overview:

The contents of a pandas.Series instance can be transformed based on a mathematical function.
By calling Series.apply() method and passing either a Python function or a numpy universal function(ufunc) as the value for func parameter, the values present in the series are transformed by the applied/passed-in function.
The Series.trasnform() method is more versatile through accepting a function name, a list of function names, or a function that works with Series.Apply().

Example - Using Series.apply():

The example Python code reads a CSV file (antennas.csv) and loads the columns into a DataFrame.

Contents of the file Antennas.csv

The column containing the orientation angles is selected into a Series and apply() is called by passing the math.cos() function as the parameter. This returns a new pandas.Series with cosine values of the orientation angles.

# Example Python program to transform the values

# of a pandas.series instance by applying a function

import pandas as pds

import math

# Load the data from the cake.csv

dataFile = "./Antennas.csv";

df = pds.read_csv(dataFile);

series = df["Orientation Angle"];

cosineValues = series.apply(math.cos);

print(cosineValues);

Output:

0 -0.759688

1 -0.275163

2 -0.532833

3 -0.903692

4 -0.666938

5 -0.759688

6 0.991203

7 -0.903692

8 -0.666938

9 0.525322

10 -0.952413

Name: Orientation Angle, dtype: float64

Example - Using Series.transform():

When more than one function is passed to transform() the result is a pandas.DataFrame whose columns are produced by the functions passed in.

# Example Python program to transform the values

# of a pandas.series instance by applying multiple

# functions

import pandas as pds

import math

def radius_squared(radius):

return math.pow(radius, 2);

def radius_cubed(radius):

return math.pow(radius, 2);

# Radius of the antennas in meters

radius_Vals = (5, 5.5, 7, 7.5, 9);

series = pds.Series(radius_Vals);

radiusTakenToPower = series.transform([radius_squared, radius_cubed]);

print(radiusTakenToPower);

print(type(radiusTakenToPower));

Output:

radius_squared radius_cubed

0 25.00 25.00

1 30.25 30.25

2 49.00 49.00

3 56.25 56.25

4 81.00 81.00