Pandas pd.melt example

Convert data from Wide-format to Long-format

import pandas as pd
import seaborn as sns
from IPython.display import display

Load Wide-format Data

df = sns.load_dataset('iris')
print "Wide-format Dataframe shape: ", df.shape
display(df.head())

Wide-format Dataframe shape:  (150, 5)
sepal_length sepal_width petal_length petal_width species
0 5.1 3.5 1.4 0.2 setosa
1 4.9 3.0 1.4 0.2 setosa
2 4.7 3.2 1.3 0.2 setosa
3 4.6 3.1 1.5 0.2 setosa
4 5.0 3.6 1.4 0.2 setosa

Convert to Long-format

df_long = pd.melt(df, id_vars="species")

print "Long-format Dataframe shape: ", df_long.shape
display(df_long.head())

 Long-format Dataframe shape:  (600, 3)
species variable value
0 setosa sepal_length 5.1
1 setosa sepal_length 4.9
2 setosa sepal_length 4.7
3 setosa sepal_length 4.6
4 setosa sepal_length 5.0

Change Variable Name

df_long = pd.melt(df, id_vars="species", var_name="measurement")

print "Long-format Dataframe shape: ", df_long.shape
display(df_long.head())

Long-format Dataframe shape:  (600, 3)
species measurement value
0 setosa sepal_length 5.1
1 setosa sepal_length 4.9
2 setosa sepal_length 4.7
3 setosa sepal_length 4.6
4 setosa sepal_length 5.0

Reference