pandas一些常用函数的使用和理解

Posted 2022-02-19 Icy Hunter

pandas库的一些用法

• 1.创建DataFrame
• 2.dataframe.columns(更改列名)
• 3.dataframe列索引、行索引
• 4.pd.read_csv()、dataframe.to_csv()
• 5.dataframe.sort_value()
• 6.dataframe.describe()

1.创建DataFrame

import pandas as pd
import numpy as np
f = pd.DataFrame(np.arange(20).reshape(4, 5), index=["c", "a", "d", "b"])
print(f)

结果

2.dataframe.columns(更改列名)

import pandas as pd
import numpy as np
f = pd.DataFrame(np.arange(20).reshape(4, 5), index=["c", "a", "d", "b"])
f.columns = ["A", "B", "C", "D", "E"]
print(f)

结果

3.dataframe列索引、行索引

import pandas as pd
import numpy as np
f = pd.DataFrame(np.arange(20).reshape(4, 5), index=["c", "a", "d", "b"])
print("f[0]:")
print(f[0])
f.columns = ["A", "B", "C", "D", "E"]
print('f["A"]')
print(f["A"])
print('f.loc["c"]')
print(f.loc["c"])

结果

4.pd.read_csv()、dataframe.to_csv()

读存取csv文件，十分方便

import pandas as pd
import numpy as np
f = pd.DataFrame(np.arange(20).reshape(4, 5), index=["c", "a", "d", "b"])
f.columns = ["A", "B", "C", "D", "E"]
f.to_csv("a.csv", index=0, encoding="utf-8")  # 行索引不保存
#  f.to_csv("a.csv", encoding="utf_8_sig")  # 这个保存用excel打开中文不会乱码
ff = pd.read_csv("a.csv", encoding="utf-8", sep=",") # 默认就是逗号相隔，sep="\\t"就可以读tsv了

print(ff)

csv文件

5.dataframe.sort_value()

对列值进行排序，ascending=False表示降序排

import pandas as pd
import numpy as np
f = pd.DataFrame(np.arange(20).reshape(4, 5), index=["c", "a", "d", "b"])
f.columns = ["A", "B", "C", "D", "E"]
f.iloc[0][1] = 20
f = f.sort_values(by=["A", "B"], ascending=False)  #  首先按A列降序，其次按B列降序
print(f)

结果

6.dataframe.describe()

用于计算一些常用的统计数

import pandas as pd
import numpy as np
f = pd.DataFrame(np.arange(20).reshape(4, 5), index=["c", "a", "d", "b"])
f.columns = ["A", "B", "C", "D", "E"]
f = f.describe()
print(f)

结果