lineplot with groupby in Python

sns.lineplot(x = df.groupby(df.index).mean().index,
             y = df.groupby(df.index).mean()['gross income'])



sns.relplot(data = df, x = "Item_No", y = "Width", kind = "line", aspect = 3)
mean = np.mean(df["Width"])
std = np.std(df["Width"])
plt.axhline(y = mean, color = "red", linestyle = "-")
plt.axhline(y = (mean + 3 * std), color = "red", linestyle = "-")
plt.axhline(y = (mean - 3 * std), color = "red", linestyle = "-")
plt.xticks(rotation = 45)
plt.show()