How to Combine Strings Within Groups Using Pandas groupby?

Pandas groupby: How to get a union of strings

The provided DataFrame contains three columns: A, B, and C. The goal is to group the DataFrame by column A and obtain a union of strings from column C for each group.

By default, groupby sums numeric columns, which doesn't work for strings.

Using a Custom Function

One approach is to define a function that concatenates strings within each group using the join method:

<code class="python">def f(x):
    return "{%s}" % ', '.join(x)</code>

And apply this function to the grouped DataFrame:

<code class="python">result = df.groupby('A')['C'].apply(f)</code>

This approach produces the desired output:

A
1    {This, string}
2           {is, !}
3               {a}
4          {random}

Using sum and Concatenation

Another option is to force sum to concatenate strings by modifying the data type:

<code class="python">df['C'] = df['C'].astype(str)
result = df.groupby('A')['C'].sum()</code>

This also gives the desired result.

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