 # Python | Pandas Series.cumsum () to find the cumulative sum of the Series

Pandas `Series.cumsum()` is used to find the cumulative sum of a series. Cumulatively, the length of the returned series is the same as the input, and each item is the sum of all previous items.

Syntax: Series.cumsum (axis = None, skipna = True)

Parameters:
axis: 0 or `index` for row wise operation and 1 or `columns` for column wise operation
skipna: Skips NaN addition for elements after the very next one if True.

Result type: Series

Example # 1:
This example creates a series from a Python list using the Pandas .Series () method. The list also contains Null, and the skipna parameter remains the default, which is True.

 ` # pandas module import ` ` import ` ` pandas as pd `   ` # numpy module import ` ` import ` ` numpy as np `   ` # compiling a list of values ​​` ` values ​​` ` = ` ` [` ` 3 ` `, ` ` 4 ` `, np.nan, ` ` 7 ` `, ` ` 2 ` `, ` ` 0 ` ]   ` # create a series from the list ` ` series ` ` = ` ` pd.Series (values) `   ` # calling method ` ` cumsum ` ` = ` ` series.cumsum () `   ` # display ` ` cumsum `

Exit:

` 3 7 NaN 14 16 16 dtype: float64 `

explanation
Accumulated amount — it is the sum of the current and all previous values. As shown in the output above, the addition was done as follows

` 3 3 + 4 = 7 7 + NaN = NaN 7 + 7 = 14 14 + 2 = 16 16 + 0 = 16 `

Example # 2: skipna = False
This example creates a series in the same way as the example above. But the ` skipna ` parameter remains False. Therefore, NULL values ​​will not be ignored and will be added each time it appears.

 ` # pandas module import ` ` import ` ` pandas as pd `   ` # numpy module import ` ` import ` ` numpy as np `   ` # compiling a list of values ​​` ` values ​​` ` = ` ` [` ` 1 , 20 , 13 , np.nan, 0 , 1 , 5 , 23 ] ````   # create a series from the list series = pd.Series (values)   # calling method cumsum = series.cumsum (skipna = False )   # display cumsum ```

Exit:

` 0 1.0 1 21.0 2 34.0 3 NaN 4 NaN 5 NaN 6 NaN 7 NaN dtype: float64 `

Explanation: As in As shown in the output, all values ​​after the first occurrence of NaN are also NaN, since any number + NaN is also NaN.