刚刚接触pandas的朋友，想了解数据结构，就一定要认识DataFrame，接下来给大家详细介绍！
初识DataFrame
import numpy as np import pandas as pd
data = {"name": ["Jack", "Tom", "LiSa"], "age": [20, 21, 18], "city": ["BeiJing", "TianJin", "ShenZhen"]} print(data) print("") frame = pd.DataFrame(data) # 创建DataFrame print(frame) print("") print(frame.index) # 查看行索引 print("") print(frame.columns) # 查看列索引 print("") print(frame.values) # 查看值
{'name': ['Jack', 'Tom', 'LiSa'], 'age': [20, 21, 18], 'city': ['BeiJing', 'TianJin', 'ShenZhen']} age city name 0 20 BeiJing Jack 1 21 TianJin Tom 2 18 ShenZhen LiSa RangeIndex(start=0, stop=3, step=1) Index(['age', 'city', 'name'], dtype='object') [[20 'BeiJing' 'Jack'] [21 'TianJin' 'Tom'] [18 'ShenZhen' 'LiSa']]
创建DataFrame
*** 一: 由字典创建 字典的key是列索引值可以是
1.列表
2.ndarray
3.Series
# 值是ndarray 注意: 用ndarray创建DataFrame值的个数必须相同 否则报错 data2 = {"one": np.random.rand(3), "two": np.random.rand(3) } print(data2) print("") print(pd.DataFrame(data2))
{'one': array([ 0.60720023, 0.30838024, 0.30678266]), 'two': array([ 0.21368784, 0.03797809, 0.41698718])} one two 0 0.607200 0.213688 1 0.308380 0.037978 2 0.306783 0.416987
# 值是Series--带有标签的一维数组 注意: 用Series创建DataFrame值的个数可以不同 少的值用Nan填充 data3 = {"one": pd.Series(np.random.rand(4)), "two": pd.Series(np.random.rand(5)) } print(data3) print("") df3 = pd.DataFrame(data3) print(df3) print("")
{'one': 0 0.217639 1 0.921641 2 0.898810 3 0.933510 dtype: float64, 'two': 0 0.132789 1 0.099904 2 0.723495 3 0.719173 4 0.477456 dtype: float64} one two 0 0.217639 0.132789 1 0.921641 0.099904 2 0.898810 0.723495 3 0.933510 0.719173 4 NaN 0.477456
# 值是Series--带有标签的一维数组 注意: 用Series创建DataFrame值的个数可以不同 少的值用Nan填充 data3 = {"one": pd.Series(np.random.rand(4)), "two": pd.Series(np.random.rand(5)) } print(data3) print("") df3 = pd.DataFrame(data3) print(df3) print("")
{'one': 0 0.217639 1 0.921641 2 0.898810 3 0.933510 dtype: float64, 'two': 0 0.132789 1 0.099904 2 0.723495 3 0.719173 4 0.477456 dtype: float64} one two 0 0.217639 0.132789 1 0.921641 0.099904 2 0.898810 0.723495 3 0.933510 0.719173 4 NaN 0.477456
*** 二: 通过二维数组直接创建
data = [{"one": 1, "two": 2}, {"one": 5, "two": 10, "three": 15}] # 每一个字典在DataFrame里就是一行数据 print(data) print("") df1 = pd.DataFrame(data) print(df1) print("") df2 = pd.DataFrame(data, index=list("ab"), columns=["one", "two", "three", "four"]) print(df2)
[{'one': 1, 'two': 2}, {'one': 5, 'two': 10, 'three': 15}] one three two 0 1 NaN 2 1 5 15.0 10 one two three four a 1 2 NaN NaN b 5 10 15.0 NaN
*** 三: 由字典组成的列表创建 DataFrame
# columns为字典的key index为子字典的key data = {"Jack": {"age":1, "country":"China", "sex":"man"}, "LiSa": {"age":18, "country":"America", "sex":"women"}, "Tom": {"age":20, "country":"English"}} df1 = pd.DataFrame(data) print(df1) print("") # 注意: 这里的index并不能给子字典的key(行索引)重新命名 但可以给子字典的key重新排序 若出现原数组没有的index 那么就填充NaN值 df2 = pd.DataFrame(data, index=["sex", "age", "country"]) print(df2) print("") df3 = pd.DataFrame(data, index=list("abc")) print(df3) print("") # columns 给列索引重新排序 若出现原数组没有的列索引填充NaN值 df4 = pd.DataFrame(data, columns=["Tom", "LiSa", "Jack", "TangMu"]) print(df4)
Jack LiSa Tom age 1 18 20 country China America English sex man women NaN Jack LiSa Tom sex man women NaN age 1 18 20 country China America English Jack LiSa Tom a NaN NaN NaN b NaN NaN NaN c NaN NaN NaN Tom LiSa Jack TangMu age 20 18 1 NaN country English America China NaN sex NaN women man NaN
*** 四: 由字典组成的字典
# columns为字典的key index为子字典的key data = {"Jack": {"age":1, "country":"China", "sex":"man"}, "LiSa": {"age":18, "country":"America", "sex":"women"}, "Tom": {"age":20, "country":"English"}} df1 = pd.DataFrame(data) print(df1) print("") # 注意: 这里的index并不能给子字典的key(行索引)重新命名 但可以给子字典的key重新排序 若出现原数组没有的index 那么就填充NaN值 df2 = pd.DataFrame(data, index=["sex", "age", "country"]) print(df2) print("") df3 = pd.DataFrame(data, index=list("abc")) print(df3) print("") # columns 给列索引重新排序 若出现原数组没有的列索引填充NaN值 df4 = pd.DataFrame(data, columns=["Tom", "LiSa", "Jack", "TangMu"]) print(df4)
Jack LiSa Tom age 1 18 20 country China America English sex man women NaN Jack LiSa Tom sex man women NaN age 1 18 20 country China America English Jack LiSa Tom a NaN NaN NaN b NaN NaN NaN c NaN NaN NaN Tom LiSa Jack TangMu age 20 18 1 NaN country English America China NaN sex NaN women man NaN
DataFrame索引
选择行与列
选择列 直接用df["列标签"]
df = pd.DataFrame(np.random.rand(12).reshape(3,4)*100, index = ["one", "two", "three"], columns = ["a", "b", "c", "d"]) print(df) print("") print(df["a"], " ", type(df["a"])) # 取一列 print("") print(df[["a", "c"]], " ", type(df[["a", "c"]])) # 取多列
a b c d one 92.905464 11.630358 19.518051 77.417377 two 91.107357 0.641600 4.913662 65.593182 three 3.152801 42.324671 14.030304 22.138608 one 92.905464 two 91.107357 three 3.152801 Name: a, dtype: float64 <class 'pandas.core.series.Series'> a c one 92.905464 19.518051 two 91.107357 4.913662 three 3.152801 14.030304 <class 'pandas.core.frame.DataFrame'>
选择行 不能通过标签索引 df["one"] 来选择行 要用 df.loc["one"], loc就是针对行来操作的
print(df) print("") print(df.loc["one"], " ", type(df.loc["one"])) # 取一行 print("") print(df.loc[["one", "three"]], " ", type(df.loc[["one", "three"]])) # 取不连续的多行 print("")
a b c d one 92.905464 11.630358 19.518051 77.417377 two 91.107357 0.641600 4.913662 65.593182 three 3.152801 42.324671 14.030304 22.138608 a 92.905464 b 11.630358 c 19.518051 d 77.417377 Name: one, dtype: float64 <class 'pandas.core.series.Series'> a b c d one 92.905464 11.630358 19.518051 77.417377 three 3.152801 42.324671 14.030304 22.138608 <class 'pandas.core.frame.DataFrame'>
loc支持切片索引--针对行 并包含末端 df.loc["one": "three"]
df = pd.DataFrame(np.random.rand(16).reshape(4,4)*100, index=["one", "two", "three", "four"], columns=["a", "b", "c", "d"]) print(df) print("") print(df.loc["one": "three"]) print("") print(df[: 3]) # 切片表示取连续的多行(尽量不用 免得混淆)
a b c d one 65.471894 19.137274 31.680635 41.659808 two 31.570587 45.575849 37.739644 5.140845 three 54.930986 68.232707 17.215544 70.765401 four 45.591798 63.274956 74.056045 2.466652 a b c d one 65.471894 19.137274 31.680635 41.659808 two 31.570587 45.575849 37.739644 5.140845 three 54.930986 68.232707 17.215544 70.765401 a b c d one 65.471894 19.137274 31.680635 41.659808 two 31.570587 45.575849 37.739644 5.140845 three 54.930986 68.232707 17.215544 70.765401
iloc也是对行来操作的 只不过把行标签改成了行索引 并且是不包含末端的
print(df) print("") print(df.iloc[0]) # 取一行 print("") print(df.iloc[[0,2]]) # 取不连续的多行 print("") print(df.iloc[0:3]) # 不包含末端
a b c d one 65.471894 19.137274 31.680635 41.659808 two 31.570587 45.575849 37.739644 5.140845 three 54.930986 68.232707 17.215544 70.765401 four 45.591798 63.274956 74.056045 2.466652 a 65.471894 b 19.137274 c 31.680635 d 41.659808 Name: one, dtype: float64 a b c d one 65.471894 19.137274 31.680635 41.659808 three 54.930986 68.232707 17.215544 70.765401 a b c d one 65.471894 19.137274 31.680635 41.659808 two 31.570587 45.575849 37.739644 5.140845 three 54.930986 68.232707 17.215544 70.765401
布尔型索引
df = pd.DataFrame(np.random.rand(16).reshape(4,4)*100, index=["one", "two", "three", "four"], columns=["a", "b", "c", "d"]) print(df) print("") d1 = df >50 # d1为布尔型索引 print(d1) print("") print(df[d1]) # df根据d1 只返回True的值 False的值对应为NaN print("")
a b c d one 91.503673 74.080822 85.274682 80.788609 two 49.670055 42.221393 36.674490 69.272958 three 78.349843 68.090150 22.326223 93.984369 four 79.057146 77.687246 32.304265 0.567816 a b c d one True True True True two False False False True three True True False True four True True False False a b c d one 91.503673 74.080822 85.274682 80.788609 two NaN NaN NaN 69.272958 three 78.349843 68.090150 NaN 93.984369 four 79.057146 77.687246 NaN NaN
选取某一列作为布尔型索引 返回True所在行的所有列 注意: 不能选取多列作为布尔型索引
df = pd.DataFrame(np.random.rand(16).reshape(4,4)*100, index=["one", "two", "three", "four"], columns=["a", "b", "c", "d"], dtype=np.int64) print(df) print("") d2 = df["b"] > 50 print(d2) print("") print(df[d2])
a b c d one 27 18 47 61 two 26 35 16 78 three 80 98 94 41 four 85 3 47 90 one False two False three True four False Name: b, dtype: bool a b c d three 80 98 94 41
选取多列作为布尔型索引 返回True所对应的值 False对应为NaN 没有的列全部填充为NaN
df = pd.DataFrame(np.random.rand(16).reshape(4,4)*100, index=["one", "two", "three", "four"], columns=["a", "b", "c", "d"], dtype=np.int64) print(df) print("") d3 = df[["a", "c"]] > 50 print(d3) print("") print(df[d3])
a b c d one 49 82 32 39 two 78 2 24 84 three 6 84 84 69 four 21 89 16 77 a c one False False two True False three False True four False False a b c d one NaN NaN NaN NaN two 78.0 NaN NaN NaN three NaN NaN 84.0 NaN four NaN NaN NaN NaN
多重索引
print(df)
a b c d one 49 82 32 39 two 78 2 24 84 three 6 84 84 69 four 21 89 16 77
print(df["a"].loc[["one", "three"]]) # 取列再取行 print("") print(df[["a", "c"]].iloc[0:3])
one 49 three 6 Name: a, dtype: int64 a c one 49 32 two 78 24 three 6 84
print(df.loc[["one", "three"]][["a", "c"]]) # 取行再取列
a c one 49 32 three 6 84
print(df > 50) print("") print(df[df>50]) print("") print(df[df>50][["a","b"]])
a b c d one False True False False two True False False True three False True True True four False True False True a b c d one NaN 82.0 NaN NaN two 78.0 NaN NaN 84.0 three NaN 84.0 84.0 69.0 four NaN 89.0 NaN 77.0 a b one NaN 82.0 two 78.0 NaN three NaN 84.0 four NaN 89.0
DataFrame基本技巧
import numpy as np import pandas as pd
arr = np.random.rand(16).reshape(8, 2)*10 # print(arr) print("") print(len(arr)) print("") df = pd.DataFrame(arr, index=[chr(i) for i in range(97, 97+len(arr))], columns=["one", "two"]) print(df)
8 one two a 2.129959 1.827002 b 8.631212 0.423903 c 6.262012 3.851107 d 6.890305 9.543065 e 6.883742 3.643955 f 2.740878 6.851490 g 6.242513 7.402237 h 9.226572 3.179664
查看数据
print(df) print("") print(df.head(2)) # 查看头部数据 默认查看5条 print("") print(df.tail(3)) # 查看末尾数据 默认查看5条
one two a 2.129959 1.827002 b 8.631212 0.423903 c 6.262012 3.851107 d 6.890305 9.543065 e 6.883742 3.643955 f 2.740878 6.851490 g 6.242513 7.402237 h 9.226572 3.179664 one two a 2.129959 1.827002 b 8.631212 0.423903 one two f 2.740878 6.851490 g 6.242513 7.402237 h 9.226572 3.179664
转置
print(df)
one two a 2.129959 1.827002 b 8.631212 0.423903 c 6.262012 3.851107 d 6.890305 9.543065 e 6.883742 3.643955 f 2.740878 6.851490 g 6.242513 7.402237 h 9.226572 3.179664
print(df.T)
a b c d e f g \ one 2.129959 8.631212 6.262012 6.890305 6.883742 2.740878 6.242513 two 1.827002 0.423903 3.851107 9.543065 3.643955 6.851490 7.402237 h one 9.226572 two 3.179664
添加与修改
df = pd.DataFrame(np.random.rand(16).reshape(4,4),index=["one", "two", "three", "four"], columns=["a", "b", "c", "d"]) print(df) print("") df.loc["five"] = 100 # 增加一行 print(df) print("") df["e"] = 10 # 增加一列 print(df) print("") df["e"] = 101 # 修改一列 print(df) print("") df.loc["five"] = 111 # 修改一行 print(df) print("")
a b c d one 0.708481 0.285426 0.355058 0.990070 two 0.199559 0.733047 0.322982 0.791169 three 0.198043 0.801163 0.356082 0.857501 four 0.430182 0.020549 0.896011 0.503088 a b c d one 0.708481 0.285426 0.355058 0.990070 two 0.199559 0.733047 0.322982 0.791169 three 0.198043 0.801163 0.356082 0.857501 four 0.430182 0.020549 0.896011 0.503088 five 100.000000 100.000000 100.000000 100.000000 a b c d e one 0.708481 0.285426 0.355058 0.990070 10 two 0.199559 0.733047 0.322982 0.791169 10 three 0.198043 0.801163 0.356082 0.857501 10 four 0.430182 0.020549 0.896011 0.503088 10 five 100.000000 100.000000 100.000000 100.000000 10 a b c d e one 0.708481 0.285426 0.355058 0.990070 101 two 0.199559 0.733047 0.322982 0.791169 101 three 0.198043 0.801163 0.356082 0.857501 101 four 0.430182 0.020549 0.896011 0.503088 101 five 100.000000 100.000000 100.000000 100.000000 101 a b c d e one 0.708481 0.285426 0.355058 0.990070 101 two 0.199559 0.733047 0.322982 0.791169 101 three 0.198043 0.801163 0.356082 0.857501 101 four 0.430182 0.020549 0.896011 0.503088 101 five 111.000000 111.000000 111.000000 111.000000 111
删除 del(删除行)/drop(删除列 指定axis=1删除行)
df = pd.DataFrame(np.random.rand(16).reshape(4,4),index=["one", "two", "three", "four"], columns=["a", "b", "c", "d"]) print(df) print("") del df["a"] # 删除列 改变原数组 print(df)
a b c d one 0.339979 0.577661 0.108308 0.482164 two 0.374043 0.102067 0.660970 0.786986 three 0.384832 0.076563 0.529472 0.358780 four 0.938592 0.852895 0.466709 0.938307 b c d one 0.577661 0.108308 0.482164 two 0.102067 0.660970 0.786986 three 0.076563 0.529472 0.358780 four 0.852895 0.466709 0.938307
df = pd.DataFrame(np.random.rand(16).reshape(4,4),index=["one", "two", "three", "four"], columns=["a", "b", "c", "d"]) print(df) print("") d1 = df.drop("one") # 删除行 并返回新的数组 不改变原数组 print(d1) print("") print(df)
a b c d one 0.205438 0.324132 0.401131 0.368300 two 0.471426 0.671785 0.837956 0.097416 three 0.888816 0.451950 0.137032 0.568844 four 0.524813 0.448306 0.875787 0.479477 a b c d two 0.471426 0.671785 0.837956 0.097416 three 0.888816 0.451950 0.137032 0.568844 four 0.524813 0.448306 0.875787 0.479477 a b c d one 0.205438 0.324132 0.401131 0.368300 two 0.471426 0.671785 0.837956 0.097416 three 0.888816 0.451950 0.137032 0.568844 four 0.524813 0.448306 0.875787 0.479477
df = pd.DataFrame(np.random.rand(16).reshape(4,4),index=["one", "two", "three", "four"], columns=["a", "b", "c", "d"]) print(df) print("") d2 = df.drop("a", axis=1) # 删除列 返回新的数组 不会改变原数组 print(d2) print("") print(df)
a b c d one 0.939552 0.613218 0.357056 0.534264 two 0.110583 0.602123 0.990186 0.149132 three 0.756016 0.897848 0.176100 0.204789 four 0.655573 0.819009 0.094322 0.656406 b c d one 0.613218 0.357056 0.534264 two 0.602123 0.990186 0.149132 three 0.897848 0.176100 0.204789 four 0.819009 0.094322 0.656406 a b c d one 0.939552 0.613218 0.357056 0.534264 two 0.110583 0.602123 0.990186 0.149132 three 0.756016 0.897848 0.176100 0.204789 four 0.655573 0.819009 0.094322 0.656406
排序
根据指定列的列值排序 同时列值所在的行也会跟着移动 .sort_values(['列'])
# 单列 df = pd.DataFrame(np.random.rand(16).reshape(4,4), columns=["a", "b", "c", "d"]) print(df) print("") print(df.sort_values(['a'])) # 默认升序 print("") print(df.sort_values(['a'], ascending=False)) # 降序
a b c d 0 0.616386 0.416094 0.072445 0.140167 1 0.263227 0.079205 0.520708 0.866316 2 0.665673 0.836688 0.733966 0.310229 3 0.405777 0.090530 0.991211 0.712312 a b c d 1 0.263227 0.079205 0.520708 0.866316 3 0.405777 0.090530 0.991211 0.712312 0 0.616386 0.416094 0.072445 0.140167 2 0.665673 0.836688 0.733966 0.310229 a b c d 2 0.665673 0.836688 0.733966 0.310229 0 0.616386 0.416094 0.072445 0.140167 3 0.405777 0.090530 0.991211 0.712312 1 0.263227 0.079205 0.520708 0.866316
根据索引排序 .sort_index()
df = pd.DataFrame(np.random.rand(16).reshape(4,4), index=[2,1,3,0], columns=["a", "b", "c", "d"]) print(df) print("") print(df.sort_index()) # 默认升序 print("") print(df.sort_index(ascending=False)) # 降序
a b c d 2 0.669311 0.118176 0.635512 0.248388 1 0.752321 0.935779 0.572554 0.274019 3 0.701334 0.354684 0.592998 0.402686 0 0.548317 0.966295 0.191219 0.307908 a b c d 0 0.548317 0.966295 0.191219 0.307908 1 0.752321 0.935779 0.572554 0.274019 2 0.669311 0.118176 0.635512 0.248388 3 0.701334 0.354684 0.592998 0.402686 a b c d 3 0.701334 0.354684 0.592998 0.402686 2 0.669311 0.118176 0.635512 0.248388 1 0.752321 0.935779 0.572554 0.274019 0 0.548317 0.966295 0.191219 0.307908
df = pd.DataFrame(np.random.rand(16).reshape(4,4), index=["x", "z", "y", "t"], columns=["a", "b", "c", "d"]) print(df) print("") print(df.sort_index()) # 根据字母顺序表排序
a b c d x 0.717421 0.206383 0.757656 0.720580 z 0.969988 0.551812 0.210200 0.083031 y 0.956637 0.759216 0.350744 0.335287 t 0.846718 0.207411 0.936231 0.891330 a b c d t 0.846718 0.207411 0.936231 0.891330 x 0.717421 0.206383 0.757656 0.720580 y 0.956637 0.759216 0.350744 0.335287 z 0.969988 0.551812 0.210200 0.083031
df = pd.DataFrame(np.random.rand(16).reshape(4,4), index=["three", "one", "four", "two"], columns=["a", "b", "c", "d"]) print(df) print("") print(df.sort_index()) # 根据单词首字母排序
a b c d three 0.173818 0.902347 0.106037 0.303450 one 0.591793 0.526785 0.101916 0.884698 four 0.685250 0.364044 0.932338 0.668774 two 0.240763 0.260322 0.722891 0.634825 a b c d four 0.685250 0.364044 0.932338 0.668774 one 0.591793 0.526785 0.101916 0.884698 three 0.173818 0.902347 0.106037 0.303450 two 0.240763 0.260322 0.722891 0.634825
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