Pandas one-liner to return column data of head output

February 25, 2022

I have a large DF with a list of projects and what phases are available for the project.

import pandas as pd
projects = {
    'phase': [1, 1, 1, 2, 1, 2, 1],
    'projID': ["foo","foo","foo","bar","foo","bar","foo"]
}
df = pd.DataFrame(projects)

I wish to return a list of all the project rows where the projID is "bar", but all I have is the phase number (2). So I have a lookup DF that lets me convert the data phase number to the projID:

lookup = {"phase":[1,2], "pname": ["bob","frank"]}
df_tmp = pd.DataFrame(lookup)
_data_phase = 2
pn = df_tmp.loc[df_tmp['phase'] == _data_phase ,'pname'].head(1)

Q1: I want pn to be the value ‘frank’ as a string, but instead it contains a DataFrame that look like this:

1    frank
Name: pname, dtype: object

How do I convert that to just the string "frank"? And can that be done as a one-liner?

Q2: Is there a better way to extract the rows from project (df) where _data_phase = x ?

>Solution :

You can simply add the .values method or [0]. Kindly try:

pn = df_tmp.loc[df_tmp['phase'] == _data_phase ,'pname'].values[0]

I think that is slicing the dataframe with the specified criteria is a good to get what you need, I wouldn’t change it! (You can use other options such as df.query().