一、添加元素
新增列/行并赋值
import numpy as np
import pandas as pd
df = pd.DataFrame(np.random.rand(16).reshape(4, 4) * 100,
columns=['a', 'b', 'c', 'd'])
print("df = \n", df)
print("-" * 100)
# 新增列/行并赋值
df['e'] = 10
df.loc[4] = 20
print("df = \n", df)
打印结果：
df =
a b c d
0 39.621173 36.363400 21.042923 36.160210
1 39.775787 32.010771 86.375488 15.035171
2 49.328983 58.402799 12.979410 59.408702
3 21.167906 91.684124 22.953356 98.618665
----------------------------------------------------------------------------------------------------
df =
a b c d e
0 39.621173 36.363400 21.042923 36.160210 10
1 39.775787 32.010771 86.375488 15.035171 10
2 49.328983 58.402799 12.979410 59.408702 10
3 21.167906 91.684124 22.953356 98.618665 10
4 20.000000 20.000000 20.000000 20.000000 20
二、修改元素
import numpy as np
import pandas as pd
df = pd.DataFrame(np.random.rand(16).reshape(4, 4) * 100,
columns=['a', 'b', 'c', 'd'])
print("df = \n", df)
print("-" * 100)
# 索引后直接修改值
df[['a', 'c']] = 100
print("df = \n", df)
打印结果：
df =
a b c d
0 39.621173 36.363400 21.042923 36.160210
1 39.775787 32.010771 86.375488 15.035171
2 49.328983 58.402799 12.979410 59.408702
3 21.167906 91.684124 22.953356 98.618665
----------------------------------------------------------------------------------------------------
df =
a b c d e
0 100 36.363400 100 36.160210 10
1 100 32.010771 100 15.035171 10
2 100 58.402799 100 59.408702 10
3 100 91.684124 100 98.618665 10
4 100 20.000000 100 20.000000 20
三、删除：del / drop()
删除：del / drop()
- del：为原地删除
- df.drop([1, 2]：返回新对象，其中的索引为名词索引而非位置下标索引
import numpy as np
import pandas as pd
# 删除 del / drop()
df = pd.DataFrame(np.random.rand(16).reshape(4, 4) * 100,
index=[2, 1, 3, 0],
columns=['a', 'b', 'c', 'd'])
print("df = \n", df)
print("-" * 50)
# del语句 - 删除列
del df['a']
print("删除第a列后：df = \n", df)
print("-" * 100)
# drop()删除行，inplace=False → 删除后生成新的数据，不改变原数据
df2 = df.drop(0)
df3 = df.drop([1, 2])
print("df = \n", df)
print("-" * 50)
print("删除第0行后：df2 = \n", df2)
print("-" * 50)
print("删除第1、2行后：df3 = \n", df3)
print("-" * 100)
# drop()删除列，需要加上axis = 1，inplace=False → 删除后生成新的数据，不改变原数据
df4 = df.drop(['d'], axis=1)
print("df = \n", df)
print("-" * 50)
print("df4 = \n", df4)
打印结果：
df =
a b c d
2 97.538939 28.115040 25.287657 82.030868
1 58.227305 40.422558 58.629622 19.732153
3 39.179936 57.157078 33.694614 68.138918
0 57.069357 35.340227 91.023129 69.587282
--------------------------------------------------
删除第a列后：df =
b c d
2 28.115040 25.287657 82.030868
1 40.422558 58.629622 19.732153
3 57.157078 33.694614 68.138918
0 35.340227 91.023129 69.587282
----------------------------------------------------------------------------------------------------
df =
b c d
2 28.115040 25.287657 82.030868
1 40.422558 58.629622 19.732153
3 57.157078 33.694614 68.138918
0 35.340227 91.023129 69.587282
--------------------------------------------------
删除第0行后：df2 =
b c d
2 28.115040 25.287657 82.030868
1 40.422558 58.629622 19.732153
3 57.157078 33.694614 68.138918
--------------------------------------------------
删除第1、2行后：df3 =
b c d
3 57.157078 33.694614 68.138918
0 35.340227 91.023129 69.587282
----------------------------------------------------------------------------------------------------
df =
b c d
2 28.115040 25.287657 82.030868
1 40.422558 58.629622 19.732153
3 57.157078 33.694614 68.138918
0 35.340227 91.023129 69.587282
--------------------------------------------------
df4 =
b c
2 28.115040 25.287657
1 40.422558 58.629622
3 57.157078 33.694614
0 35.340227 91.023129
Process finished with exit code 0
