# pandas groupby sum with code examples

Pandas is a versatile and powerful data manipulation library for Python that allows you to work with data in ways that many other tools cannot. One of the most useful features of Pandas is its ability to group data by specified criteria, and then perform aggregate calculations on the groups. In this article, we will discuss how to perform a "groupby sum" in Pandas and provide several examples to help you get started.

The Basics of Groupby Sum in Pandas

The "groupby" method in Pandas is a way to group data based on specified columns or criteria. Once a group is formed, you can perform various operations on the groups, such as calculating the sum, mean, standard deviation, and more. The basic syntax for groupby is:

```df.groupby(by=grouping_columns)[columns_to_sum].sum()
```
• The `by` parameter specifies the column or criteria to group by. This can be a single column or a list of columns.
• The `columns_to_sum` parameter specifies the columns to sum for each group. This can be a single column or a list of columns.

Now let's look at some examples of how you can use the groupby sum function to analyze data in Pandas.

Code Examples of Groupby Sum in Pandas

Example 1: Groupby Sum on a Single Column

Suppose we have a dataframe of sales data for different products in different states. We want to group the data by the state column and calculate the total sales for each state. Here's the code to do that:

```import pandas as pd

# Create a dataframe of sales data
data = {'state': ['CA', 'TX', 'NY', 'CA', 'TX'],
'product': ['A', 'B', 'A', 'B', 'A'],
'sales': [100, 200, 150, 250, 120]}
sales_df = pd.DataFrame(data)

# Group and sum the sales data by state
sales_by_state = sales_df.groupby(by='state')['sales'].sum()

print(sales_by_state)
```

Output:

```state
CA    350
NY    150
TX    320
Name: sales, dtype: int64
```

In this example, we first create a dataframe of sales data with three columns: state, product, and sales. We then group the data by the state column and calculate the sum of sales for each state. The resulting output shows the total sales for each state.

Example 2: Groupby Sum on Multiple Columns

Now let's consider a slightly more complex example where we want to group data by multiple columns and calculate the sum of sales for each group. We will use the same sales dataframe as in Example 1, but this time we will group it by both state and product.

```import pandas as pd

# Create a dataframe of sales data
data = {'state': ['CA', 'TX', 'NY', 'CA', 'TX'],
'product': ['A', 'B', 'A', 'B', 'A'],
'sales': [100, 200, 150, 250, 120]}
sales_df = pd.DataFrame(data)

# Group and sum the sales data by state and product
sales_by_state_product = sales_df.groupby(by=['state', 'product'])['sales'].sum()

print(sales_by_state_product)
```

Output:

```state  product
CA     A          100
B          250
NY     A          150
TX     A          120
B          200
Name: sales, dtype: int64
```

In this example, we group the sales data by both state and product columns. The resulting output shows the total sales for each combination of state and product.

Example 3: Groupby Sum with Group Labeling

Sometimes it is useful to give labels to the groups that are produced by `groupby`. This can make it easier to identify the groups when working with the data later. Here's an example of how to assign labels to the groups using the `groupby` method.

```import pandas as pd

# Create a dataframe of sales data
data = {'state': ['CA', 'TX', 'NY', 'CA', 'TX'],
'product': ['A', 'B', 'A', 'B', 'A'],
'sales': [100, 200, 150, 250, 120]}
sales_df = pd.DataFrame(data)

# Group and sum the sales data by state and product
sales_by_state_product = sales_df.groupby(by=['state', 'product'], as_index=False)['sales'].sum()

print(sales_by_state_product)
```

Output:

```  state product  sales
0    CA       A    100
1    CA       B    250
2    NY       A    150
3    TX       A    120
4    TX       B    200
```

In this example, we add the `as_index=False` parameter to the `groupby` method to create a new dataframe with columns for each group. The resulting output shows the total sales for each combination of state and product with a unique label.

Conclusion

let's dive a bit deeper into the two main concepts we discussed earlier: the `groupby` method and the `sum` function.

Groupby Method

The `groupby` method in Pandas is a powerful tool that allows you to group your data based on specific criteria. This can be done on one or multiple columns and can help to reveal important insights in your data. When you group data using `groupby`, you create groups based on the unique values in the specified column(s).

The basic syntax for `groupby` is:

```df.groupby(by=grouping_columns)
```
• The `by` parameter specifies the column(s) to group by. This can be a single column or a list of columns.

Once you have created the groups, you can perform various operations on them. These include calculating aggregates like the sum, mean, median, mode, variance, and standard deviation, as well as other operations like count, max, and min.

Sum Function

The `sum` function in Pandas is an aggregate function that can be used to calculate the sum of elements in a column or row. When combined with `groupby`, it can help you quickly calculate the sum of groups based on specified criteria.

The basic syntax for using `sum` with `groupby` is:

```df.groupby(by=grouping_columns)['column_to_sum'].sum()
```
• The `by` parameter specifies the column(s) to group by. This can be a single column or a list of columns.
• The `['column_to_sum']` parameter specifies the column to sum for each group.

After running this code, you should see the total sum for each group in the specified column.

How Groupby and Sum Work Together

The `groupby` and `sum` functions work together to help you summarize your data and find important insights. When you group a dataset by a specific column or columns, you create subgroups of that original dataset. When you then apply `sum` to that grouping, you can find the total sum for each of the subgroups.

For example, let's say you have a dataset that includes information about customer purchases in different cities. You could use `groupby` to group the data by city, and then use `sum` to find the total sales for each city. This would allow you to quickly see which cities are the most profitable, and where there may be opportunities for growth.

In conclusion, using the `groupby` and `sum` methods in Pandas can help you to quickly summarize and analyze your data. By grouping your data based on specified criteria and then calculating the sum of elements in each group, you can quickly identify important insights and trends in your data.

## Popular questions

1. What is the purpose of the `groupby` function in Pandas?
• The `groupby` function in Pandas is used to group data based on specific criteria, such as unique values in a column. This allows for easier analysis and aggregation of data.
1. What operation can be performed on the groups created by the `groupby` function?
• Various operations can be performed on the groups created by `groupby`, including calculating aggregates like the sum, mean, median, mode, variance, and standard deviation, as well as other operations like count, max, and min.
1. How can `sum` be used in conjunction with `groupby`?
• You can use `sum` in conjunction with `groupby` to calculate the sum of values in a specific column for each group created by the `groupby` function.
1. Can you use `groupby` with multiple columns in Pandas?
• Yes, you can use `groupby` with multiple columns in Pandas. This allows you to group data by more than one factor and provides more detailed insights and analysis.
1. Does the `groupby` method modify the original DataFrame?
• No, by default the `groupby` method does not modify the original DataFrame. However, it is possible to modify the resulting groups or create a new DataFrame with modified data.

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##### Deeksha Dev
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