It is an important process of data cleaning, which can be calculated according to index alignment. If there is no alignment position, then the NaN can be filled. Finally, the NaN can also be filled

1. Series alignment by row and index

Example code:

s1 = pd.Series(range(10, 20), index = range(10))
s2 = pd.Series(range(20, 25), index = range(5))

print('s1: ' )
print(s1)

print('') 

print('s2: ')
print(s2)

Operation result:

s1: 
0    10
1    11
2    12
3    13
4    14
5    15
6    16
7    17
8    18
9    19
dtype: int64

s2: 
0    20
1    21
2    22
3    23
4    24
dtype: int64

2. Alignment of series

Example code:

# Series alignment
s1 + s2

Operation result:

0    30.0
1    32.0
2    34.0
3    36.0
4    38.0
5     NaN
6     NaN
7     NaN
8     NaN
9     NaN
dtype: float64

1. DataFrame is aligned by row and column index

Example code:

df1 = pd.DataFrame(np.ones((2,2)), columns = ['a', 'b'])
df2 = pd.DataFrame(np.ones((3,3)), columns = ['a', 'b', 'c'])

print('df1: ')
print(df1)

print('') 
print('df2: ')
print(df2)

Operation result:

df1: 
     a    b
0  1.0  1.0
1  1.0  1.0

df2: 
     a    b    c
0  1.0  1.0  1.0
1  1.0  1.0  1.0
2  1.0  1.0  1.0

2. Alignment of dataframe

Example code:

# DataFrame alignment operation
df1 + df2

Operation result:

     a    b   c
0  2.0  2.0 NaN
1  2.0  2.0 NaN
2  NaN  NaN NaN

1. fill_value

While using add, sub, div, mul,

Fill in value is specified by fill in value, and unaligned data will be calculated with fill in value

Example code:

print(s1)
print(s2)
s1.add(s2, fill_value = -1)

print(df1)
print(df2)
df1.sub(df2, fill_value = 2.)

Operation result:

# print(s1)
0    10
1    11
2    12
3    13
4    14
5    15
6    16
7    17
8    18
9    19
dtype: int64

# print(s2)
0    20
1    21
2    22
3    23
4    24
dtype: int64

# s1.add(s2, fill_value = -1)
0    30.0
1    32.0
2    34.0
3    36.0
4    38.0
5    14.0
6    15.0
7    16.0
8    17.0
9    18.0
dtype: float64


# print(df1)
     a    b
0  1.0  1.0
1  1.0  1.0

# print(df2)
     a    b    c
0  1.0  1.0  1.0
1  1.0  1.0  1.0
2  1.0  1.0  1.0


# df1.sub(df2, fill_value = 2.)
     a    b    c
0  0.0  0.0  1.0
1  0.0  0.0  1.0
2  1.0  1.0  1.0