How to add a column to a pandas dataframe without column? [duplicate]

Question

I have a DataFrame wich has 2 'columns'. The first column does not seem to have a column name, the second one is named Speed.

Here is a MRE:

from io import StringIO # to read strings as files for read_csv import pandas as pd parts = [ '[Level1]\nLocation = "London"\nType= "GTHY66"\n' 'Date = "16-11-2021"\nEnergy level = "Critical zero"\n', '0.000 26.788\n0.027 26.807\n0.053 26.860' ] lvl2_lines = "Speed\n" + parts[1] df_level2 = pd.read_csv(StringIO(lvl2_lines), sep='\t') print(df_level2.columns) print(df_level2)

This was my output when I did the print statements:

Index(['Speed'], dtype='object') Speed 0 0.000 26.788 1 0.027 26.807 2 0.053 26.860

This is my desired output:

Index(['Power', 'Speed'], dtype='object') Power Speed 0 0.000 26.788 1 0.027 26.807 2 0.053 26.860

It look slike you have a multiindex perhaps? Try df.reset_index() — G. Anderson
– G. Anderson, Commented Nov 17, 2021 at 19:43
@not_speshal no because I don't want to rename. I want to add because I only have one column — Al-Andalus
– Al-Andalus, Commented Nov 17, 2021 at 19:47
I already tried what @splash58 did but I received the following error: ValueError: Length mismatch: Expected axis has 1 elements, new values have 2 elements — Al-Andalus
– Al-Andalus, Commented Nov 17, 2021 at 19:50

not_speshal · Accepted Answer · 2021-11-17 19:54:00Z

1

You need to split the strings:

df[["Power", "Speed"]] = df["Speed"].str.split(expand=True).astype(float) >>> df Speed Power 0 26.788 0.000 1 26.807 0.027 2 26.860 0.053

answered Nov 17, 2021 at 19:54

not_speshal

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2 Comments

Henry Ecker Over a year ago

We could just specify both column names lvl2_lines = "Speed\n" + parts[1] -> lvl2_lines = "Power Speed\n" + parts[1] then there's no need to split after the fact or change dtype. But this would push the question into typo territory. And df_level2 = pd.read_csv(StringIO(lvl2_lines), sep=r'\s+', engine='python') to handle mixed spacing.

not_speshal Over a year ago

I see what you mean. That's a neat way to directly read correctly instead of manipulating later. I answered before OP posted that bit in his question tho :)

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