[PYTHON/PANDAS] merge 함수 : on/how 인자를 사용해 LEFT OUTER JOIN 데이터 만들기

■ merge 함수에사 on/how 인자를 사용해 LEFT OUTER JOIN 데이터를 만드는 방법을 보여준다.

▶ main.py


import pandas as pd
import numpy  as np

dataFrame1 = pd.DataFrame({"key" : ["A", "B", "C", "D"], "value" : np.random.randn(4)})
dataFrame2 = pd.DataFrame({"key" : ["B", "D", "D", "E"], "value" : np.random.randn(4)})

print(dataFrame1)

"""
  key     value
0   A -1.241331
1   B -0.767490
2   C  2.178568
3   D  0.576111
"""

print()

print(dataFrame2)

"""
  key     value
0   B -0.947082
1   D -0.126260
2   D  1.114855
3   E  0.106320
"""

print()

dataFrame3 = pd.merge(dataFrame1, dataFrame2, on = "key", how = "left") # LEFT OUTER JOIN

print(dataFrame3)

"""
  key   value_x   value_y
0   A -1.241331       NaN
1   B -0.767490 -0.947082
2   C  2.178568       NaN
3   D  0.576111 -0.126260
4   D  0.576111  1.114855
"""

import pandas as pd

import numpy as np

dataFrame1 = pd.DataFrame({"key" : ["A", "B", "C", "D"], "value" : np.random.randn(4)})

dataFrame2 = pd.DataFrame({"key" : ["B", "D", "D", "E"], "value" : np.random.randn(4)})

print(dataFrame1)

"""

key value

0 A -1.241331

1 B -0.767490

2 C 2.178568

3 D 0.576111

"""

print()

print(dataFrame2)

"""

key value

0 B -0.947082

1 D -0.126260

2 D 1.114855

3 E 0.106320

"""

print()

dataFrame3 = pd.merge(dataFrame1, dataFrame2, on = "key", how = "left") # LEFT OUTER JOIN

print(dataFrame3)

"""

key value_x value_y

0 A -1.241331 NaN

1 B -0.767490 -0.947082

2 C 2.178568 NaN

3 D 0.576111 -0.126260

4 D 0.576111 1.114855

"""

▶ requirements.txt


numpy==2.1.2
pandas==2.2.3
python-dateutil==2.9.0.post0
pytz==2024.2
six==1.16.0
tzdata==2024.2

numpy==2.1.2

pandas==2.2.3

python-dateutil==2.9.0.post0

pytz==2024.2

six==1.16.0

tzdata==2024.2

※ pip install pandas 명령을 실행했다.