how does value_counts work pandas code example

Example 1: count values pandas

>>> index = pd.Index([3, 1, 2, 3, 4, np.nan])
>>> index.value_counts()
3.0    2
4.0    1
2.0    1
1.0    1
dtype: int64

Example 2: plot value counts pandas

df.letters.value_counts().sort_values().plot(kind = 'barh')