How to Color Scatter Plots by Column Values in Python?

Coloring Scatter Plots by Column Values

In Python, the Matplotlib library provides several means of customizing scatter plot aesthetics. One common task is assigning colors based on values in a specific column.

Seaborn Integration

One solution is to leverage the Seaborn library, which builds upon Matplotlib. Seaborn offers high-level functions like sns.relplot and sns.FacetGrid that allow you to easily map scatter plots onto specific columns. By specifying the hue parameter, you can color points according to a third column containing category labels.

<code class="python">import seaborn as sns

sns.relplot(data=df, x='Weight (kg)', y='Height (cm)', hue='Gender')</code>

Directly Using Matplotlib

Alternatively, you can directly use Matplotlib's plt.scatter function to create scatter plots and specify colors manually. This requires creating a custom color dictionary that maps category labels to colors.

<code class="python">def dfScatter(df, xcol='Height', ycol='Weight', catcol='Gender'):
    fig, ax = plt.subplots()

    categories = np.unique(df[catcol])
    colors = np.linspace(0, 1, len(categories))
    colordict = dict(zip(categories, colors))

    df['Color'] = df[catcol].apply(lambda x: colordict[x])
    ax.scatter(df[xcol], df[ycol], c=df.Color)
    return fig</code>

By calling this function, you can generate a scatter plot colored by the specified category column:

<code class="python">df = pd.DataFrame({'Height': np.random.normal(size=10),
                   'Weight': np.random.normal(size=10),
                   'Gender': ["Male", "Male", "Unknown", "Male", "Male",
                              "Female", "Did not respond", "Unknown", "Female", "Female"]})
fig = dfScatter(df)</code>

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