Python Pandas if/else Statement

Question

I am trying to write a nested if/else statement using pandas, but not very great with if statements in pandas. Please find the sample CSV data being processed and the sample code snippet I've written so far.

df:

Current if/else statement logic:

import pandas as pd

df = pd.read_csv('file.csv', sep=';')

def get_cost(df):
    t_zone = 720
    max_rate = 5.5
    rate = 0.0208
    duration = df['t1']

    if duration < t_zone:
        if(duration * rate) >= max_rate:
            return max_rate
        else:
            return(duration * rate)
    else:
        if duration >= 720:
            x = int(duration/720)
            y = ((duration%720) * rate)
            if y >= max_rate:
                return((x * max_rate) + max_rate)
            else:
                return((x * max_rate) + y)

cost = get_cost(df)

This snippet raises a ValueError: The truth value of a Series is ambiguous error. If anyone has better solutions or could help translate this if/else statement a more pandas way that would be amazing!

Hi @TomWojcik are you referring to find where the error is coming from? — mm_nieder
– mm_nieder, Commented Aug 21, 2018 at 14:55

DYZ · Accepted Answer · 2018-08-21 15:12:34Z

4

It is not efficient to use loops and if statements in pandas, unless absolutely necessary. Here is a completely vectorized, 100% pandas solution:

import numpy as np # Needs numpy, too
x = df['t1'] // 720 * max_rate # Note the use of //!
y = df['t1'] %  720 * rate
df['cost'] = np.where(df['t1'] < t_zone, 
                      np.minimum(df['t1'] * rate, max_rate),
                      np.minimum(y,               max_rate) + x)

edited Aug 21, 2018 at 15:12

answered Aug 21, 2018 at 15:06

DYZ

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Comments

V Sree Harissh · Accepted Answer · 2018-08-21 14:56:07Z

2

Try this solution.

import pandas as pd

df = pd.read_csv('file.csv')

def get_cost(x):
    t_zone = 720
    max_rate = 5.5
    rate = 0.0208
    duration = x['t1']
    if duration < t_zone:
        if(duration * rate) >= max_rate:
            return max_rate
        else:
            return(duration * rate)
    else:
        if duration >= 720:
            x = int(duration/720)
            y = ((duration%720) * rate)
            if y >= max_rate:
                return((x * max_rate) + max_rate)
            else:
                return((x * max_rate) + y)

df['cost'] = df.apply(get_cost, axis=1)

You could also assign result to the same column too. In this case, I have assigned to a custom column called 'cost'.

Output:

    t1  cost
0   8   0.1664
1   1134    11.0000
2   0   0.0000
3   119 2.4752
4   122 2.5376
5   446 5.5000
6   21  0.4368
7   0   0.0000
8   138 2.8704
9   0   0.0000

answered Aug 21, 2018 at 14:56

V Sree Harissh

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2 Comments

mm_nieder Over a year ago

thank you so much for you help. This was exactly what i needed!

V Sree Harissh Over a year ago

Kindly accept the answer in case this was what you were looking for. :)

Interested_Programmer · Accepted Answer · 2018-08-21 15:01:47Z

You should be iterating over the duration rather than directly comparing it to a number. You could do this.

import pandas as pd

df = pd.read_csv('file.csv', sep=';')

def get_cost(df):
    t_zone = 720
    max_rate = 5.5
    rate = 0.0208
    duration = df['t1']
    ratecol = []
    for i in duration:
        if i < t_zone:
            if(i * rate) >= max_rate:
                ratecol.append(max_rate)
            else:
                ratecol.append(i * rate)
        else:
            if i >= 720:
                x = int(i/720)
                y = ((i%720) * rate)
                if y >= max_rate:
                    ratecol.append((x * max_rate) + max_rate)
                else:
                    ratecol.append((x * max_rate) + y)
    return ratecol
df['cost'] = get_cost(df)

This code produces exact same result as the one posted before.

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