> For the complete documentation index, see [llms.txt](https://larhues-personal-organization.gitbook.io/intro-to-data-visualization/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://larhues-personal-organization.gitbook.io/intro-to-data-visualization/getting-started/aggregating-data.md).

# Aggregating Data

The `groupby` and `aggregate` methods in pandas are powerful tools for summarizing and aggregating data within a DataFrame. The `groupby` method allows you to group rows based on the values in one or more columns, creating subsets of the data that share the same group label. Once grouped, the `aggregate` function can be applied to calculate summary statistics, such as sums, means, counts, or custom computations for each group. For example, in a sales dataset, you can use `groupby` on a "Region" column and aggregate by summing the "Sales" column to find total sales per region. This approach is highly efficient and flexible.

One of the strengths of combining `groupby` with `aggregate` is its versatility. You can apply multiple aggregation functions simultaneously to different columns using a dictionary-like syntax. For instance, in a dataset with columns "Date," "Sales," and "Profit," you can group by "Date" and compute both the total sales (`sum`) and average profit (`mean`) in a single step. Additionally, custom functions can be applied using Python's lambda expressions or user-defined functions, enabling complex and tailored calculations. This functionality is invaluable in exploratory data analysis and preprocessing tasks, where quickly summarizing and reshaping data is essential for uncovering patterns and preparing data for further analysis or visualization.

Let's get started with the tips dataset.

```python
import plotly.express as px
import pandas as pd

# Download the tips dataset
df = px.data.tips()


df_grouped = df.groupby(['sex']).agg({'total_bill': 'sum'})
df_grouped.reset_index(inplace=True)
df_grouped.head()

fig = px.bar(df_grouped, x="sex", y="total_bill") 

fig.show()
```