# Groupby 2 categorical variables

## All we need is an easy explanation of the problem, so here it is.

I have a dataframe that looks like this:

ID memory confidence Test (1= correct, 2=incorrect) Experiment
1 56 1 Experiment 1
1 78 0 Experiment 1
1 98 0 Experiment 1
1 24 1 Experiment 2
2 45 0 Experiment 2
2 87 1 Experiment 2

I want to see if a person’s average confidence is correlated with their performance on the test. So I have written the following code, which shows a persons average memory confidence, and their average score:

df3 = df.groupby([‘PID’])[‘accuracy’,’memory_confidence’].mean()

i = sns.lmplot(x = ‘memory_confidence’, y = ‘accuracy’, data = df3)

What I want to do now is to compute different correlations/ lmplots for Experiment 1 and Experiment 2

adding in ‘source’ does not work, as I get KeyError: "[‘source’] not in index"

df3 = df.groupby([‘PID’,‘source’])[‘accuracy’,’memory_confidence’].mean()

i = sns.lmplot(x = ‘memory_confidence’, y = ‘accuracy’, hue=’source’, data = df3)

## How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

### Method 1

``````import numpy as np
import pandas as pd

df = pd.DataFrame([
[1, 56, 1,  'Experiment 1'],
[1, 78, 0,  'Experiment 1'],
[1, 98, 0,  'Experiment 1'],
[1, 24, 1,  'Experiment 2'],
[2, 45, 0,  'Experiment 2'],
[2, 87, 1,  'Experiment 2']
], columns=['ID', 'memory_confidence', 'accuracy', 'Experiment'])

sns.lmplot(x = 'memory_confidence', y = 'accuracy', hue='Experiment', data=df)
plt.show()

exp1 = df[df['Experiment'] == 'Experiment 1']
exp1_corr = exp1.corr().loc['memory_confidence', 'accuracy']
exp2 = df[df['Experiment'] == 'Experiment 2']
exp2_corr = exp2.corr().loc['memory_confidence', 'accuracy']
print(exp1_corr, exp2_corr)
``````

Produces the following:

``````-0.8794395358869003 0.18898223650461368
``````

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂