How to select values from a CSV file depending on the value of a specific column

Question

Take this csv as an example:

Col1, Col2
1,3,
0,5,
1,4
0,7

Say that I have a list, and I want to append the values of Col2 to the list only if the value of Col1 in the same row is 1. The resulting list should be [3,4].

How can I do this with pandas without using iterrows()?

David Erickson · Accepted Answer · 2020-05-29 23:20:08Z

1

I think .loc is the most pythonic and simplest method.
```
df.loc[df['Col1'] == '1']['Col2'].to_list()
```

An alternative using np.where:

import numpy as np
df['Col3'] = np.where(df['Col1'] == 1, df['Col2'], '')
listt = list(filter(None,df['Col3'].to_list()))

zip is a loop alternative to iterrows.

listt = []
for x, y in zip(df['Col1'], df['Col2']):
    if x == 1:
        listt.append(y)

edited May 29, 2020 at 23:20

answered May 29, 2020 at 22:54

David Erickson

16.7k2 gold badges21 silver badges37 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

yoskovia · Accepted Answer · 2020-05-29 23:04:26Z

0

Assuming you've read in your csv into a dataframe named df, you could use this:

wanted = df.query('Col1 == 1')['Col2'].values
mylist.extend(wanted)

answered May 29, 2020 at 23:04

yoskovia

3602 silver badges10 bronze badges

Comments

Vaibhav Bharati · Accepted Answer · 2020-06-01 05:15:54Z

0

import pandas as pd

lst_result=[]
for ind, row in df.iterrows():
    if df.at[ind,'Col1'] == 1:
        lst_result.append(df.at(ind,['Col2']))
print(lst_result)

answered Jun 1, 2020 at 5:15

Vaibhav Bharati

343 bronze badges

2 Comments

Mark Rotteveel Over a year ago

Please don't post only code as answer, but also provide an explanation what your code does and how it solves the problem of the question. Answers with an explanation are usually more helpful and of better quality, and are more likely to attract upvotes.

SherylHohman Over a year ago

While this code may resolve the OP's issue, it is best to include an explanation as to how your code addresses the OP's issue. In this way, future visitors can learn from your post, and apply it to their own code. SO is not a coding service, but a resource for knowledge. Also, high quality, complete answers are more likely to be upvoted. These features, along with the requirement that all posts are self-contained, are some of the strengths of SO as a platform, that differentiates it from forums. You can edit to add additional info &/or to supplement your explanations with source documentation.

Collectives™ on Stack Overflow

How to select values from a CSV file depending on the value of a specific column

3 Answers 3

Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related