How to get statistics for each group (such as count, mean, max, min e.tc) using pandas GroupBy? You can achieve this by using groupby() method and agg() function.
In this article, you can learn pandas.DataFrame.groupby() to group the single column, two, or multiple columns and get the size(), count() for each group combination. groupBy() function is used to collect the identical data into groups and perform aggregate functions like size/count on the grouped data.
In Pandas, you can use groupby() with the combination of count(), size(), mean(), min(), max() and more methods.
1. Quick Examples of Pandas Get Statistics For Each Group
If you are in a hurry, below are some quick examples.
# Below are some quick examples.
# Use DataFrame.size()
df2=df.groupby(['Courses','Duration'])
df2=df.groupby(['Courses', 'Duration']).size().reset_index(name='counts'))
# Pandas groupby() with agg() Method.
df2 = df.groupby(['Courses', 'Duration']).agg(['mean', 'count'])
# Pandas Get Statistics Using groupby().describe()
df2=df.groupby(['Courses', 'Duration'])['Discount'].describe()
# Pandas DataFrame.groupby() and describe() function.
df2=df.groupby(['Courses', 'Duration'])['Discount'].describe()[['count', 'mean']]
# Get statistics by DataFrame.value_counts.
df2=df.value_counts(subset=['Courses', 'Duration'])
# Using groupby() and agg() function.
df2 = df.groupby(['Courses','Duration']).agg(['mean', 'count'])
df.columns = [ ' '.join(str(i) for i in col) for col in df.columns]
df.reset_index(inplace=True)
Now, let’s create a DataFrame with a few rows and columns, execute these examples and validate results. Our DataFrame contains column names Courses, Fee, Duration, and Discount.
# Create a DataFrame.
import pandas as pd
technologies = ({
'Courses':["Spark","PySpark","Hadoop","Python","Hadoop","Hadoop","Spark","Python","Spark"],
'Fee' :[22000,25000,23000,24000,26000,25000,25000,22000,25000],
'Duration':['30days','50days','55days', '40days','55days','35days','30days','40days','40days'],
'Discount':[1000,2300,1000,1200,2500,1200,1400,1000,1200]
})
df = pd.DataFrame(technologies)
print(df)
Yields below output.
# Output:
Courses Fee Duration Discount
0 Spark 22000 30days 1000
1 PySpark 25000 50days 2300
2 Hadoop 23000 55days 1000
3 Python 24000 40days 1200
4 Hadoop 26000 55days 2500
5 Hadoop 25000 35days 1200
6 Spark 25000 30days 1400
7 Python 22000 40days 1000
8 Spark 25000 40days 1200
2. Pandas groupby() with size() to get Column Counts
Use DataFrame.groupby() to group the rows and use size() to get the count on each group. The size property is used to get an int representing the number of elements in this object. For the Series object, it returns the number of rows. For the DataFrame object, it returns the number of rows times the number of columns (rows * columns).
# Use DataFrame.size()
df2=df.groupby(['Courses','Duration'])
df2=df.groupby(['Courses', 'Duration']).size().reset_index(name='counts')
print(df2)
Yields below output. Note the groupby() method returns the pandas.core.groupby.generic.DataFrameGroupBy. reset_index(name='counts') is used to set the label name for the size column.
# Output:
Courses Duration counts
0 Hadoop 35days 1
1 Hadoop 55days 2
2 PySpark 50days 1
3 Python 40days 2
4 Spark 30days 2
5 Spark 40days 1
3. Pandas groupby() with agg() Method
Alternatively, you can also use groupby() method and use agg() function to the size/count. The agg() method allows you to apply a function or a list of function names to be executed along with one of the axis of the DataFrame, axis by default set to 0, which is the index (row) axis.
To get the counts and mean for each group combination use count and mean aggregations.
# Pandas .groupby() and using agg() Method.
df2 = df.groupby(['Courses', 'Duration']).agg(['mean', 'count'])
print(df2)
Yields below output.
# Output:
Fee Discount
mean count mean count
Courses Duration
Hadoop 35days 25000.0 1 1200.0 1
55days 24500.0 2 1750.0 2
PySpark 50days 25000.0 1 2300.0 1
Python 40days 23000.0 2 1100.0 2
Spark 30days 23500.0 2 1200.0 2
40days 25000.0 1 1200.0 1
4. Pandas Get Statistics Using groupby().describe()
In this section, we can get statistics using groupby().describe() function. The describe() function is used as a summarization tool that quickly displays statistics for any variable or group it is applied to. The describe() output varies depending on whether you apply it to a numeric or character column.
# Pandas Get Statistics Using groupby().describe()
df2=df.groupby(['Courses', 'Duration'])['Discount'].describe()
print(df2)
Yields below output.
# Output:
count mean std ... 50% 75% max
Courses Duration ...
Hadoop 35days 1.0 1200.0 NaN ... 1200.0 1200.0 1200.0
55days 2.0 1750.0 1060.660172 ... 1750.0 2125.0 2500.0
PySpark 50days 1.0 2300.0 NaN ... 2300.0 2300.0 2300.0
Python 40days 2.0 1100.0 141.421356 ... 1100.0 1150.0 1200.0
Spark 30days 2.0 1200.0 282.842712 ... 1200.0 1300.0 1400.0
40days 1.0 1200.0 NaN ... 1200.0 1200.0 1200.0
You can just use the built-in function count() and mean() follow by the DataFrame.groupby() and describe() function.
# Pandas DataFrame.groupby() and describe() function.
df2=df.groupby(['Courses', 'Duration'])['Discount'].describe()[['count', 'mean']]
print(df2)
Yields below output.
# Output:
count mean
Courses Duration
Hadoop 35days 1.0 1200.0
55days 2.0 1750.0
PySpark 50days 1.0 2300.0
Python 40days 2.0 1100.0
Spark 30days 2.0 1200.0
40days 1.0 1200.0
5. Get Statistics of Each Group by DataFrame.value_counts
To get Pandas statistics of each group by DataFrame.value_counts. The value_counts() function is used to get a Series containing counts of unique values.
# Get statistics by DataFrame.value_counts.
df2=df.value_counts(subset=['Courses', 'Duration'])
print(df2)
Yields below output.
# Output:
Courses Duration
Hadoop 55days 2
Python 40days 2
Spark 30days 2
Hadoop 35days 1
PySpark 50days 1
Spark 40days 1
dtype: int64
6. Other Examples
In this section, To get multiple stats, collapse the index, and retain column names. For example-
# Using groupby() and agg() function.
df2 = df.groupby(['Courses','Duration']).agg(['mean', 'count'])
df.columns = [ ' '.join(str(i) for i in col) for col in df.columns]
df.reset_index(inplace=True)
print(df2)
Yields below output.
# Output:
Courses Duration
Hadoop 55days 2
Python 40days 2
Spark 30days 2
Hadoop 35days 1
PySpark 50days 1
Spark 40days 1
dtype: int64
7. Complete Examples to Get Statistics of Each Group
# Create a DataFrame.
import pandas as pd
technologies = ({
'Courses':["Spark","PySpark","Hadoop","Python","Hadoop","Hadoop","Spark","Python","Spark"],
'Fee' :[22000,25000,23000,24000,26000,25000,25000,22000,25000],
'Duration':['30days','50days','55days', '40days','55days','35days','30days','40days','40days'],
'Discount':[1000,2300,1000,1200,2500,1200,1400,1000,1200]
})
df = pd.DataFrame(technologies)
print(df)
# Use DataFrame.size()
df2=df.groupby(['Courses','Duration'])
df2=df.groupby(['Courses', 'Duration']).size().reset_index(name='counts'))
# Pandas groupby() with agg() Method.
df2 = df.groupby(['Courses', 'Duration']).agg(['mean', 'count'])
# Pandas Get Statistics Using groupby().describe()
df2=df.groupby(['Courses', 'Duration'])['Discount'].describe()
# Pandas DataFrame.groupby() and describe() function.
df2=df.groupby(['Courses', 'Duration'])['Discount'].describe()[['count', 'mean']]
# Get statistics by DataFrame.value_counts.
df2=df.value_counts(subset=['Courses', 'Duration'])
# Using groupby() and agg() function.
df2 = df.groupby(['Courses','Duration']).agg(['mean', 'count'])
df.columns = [ ' '.join(str(i) for i in col) for col in df.columns]
df.reset_index(inplace=True)
Conclusion
In this article, you have learned how to groupby() single and multiple columns and get counts, size, max, min, mean for each group from pandas DataFrame. Also, learn how to get the stats using describe() build-in function.
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