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Pythonのpandasで特定のカラムのみを選択する
pandas の DataFrame から特定の列を選択してみよう。
import pandas as pd
df = pd.read_csv('population.csv', index_col=0)
rows = df[['男', '女']]
print(rows)
結果はこうなる。
男 女
市区町村
千代田区 31,935 31,700
中央区 77,241 85,261
港 区 121,326 136,100
新宿区 173,743 172,419
文京区 105,462 116,027
台東区 101,917 97,375
墨田区 134,678 137,181
江東区 256,116 262,363
品川区 193,644 201,056
目黒区 132,206 147,136
大田区 362,653 366,881
世田谷区 431,026 477,881
渋谷区 108,768 117,826
中野区 167,378 164,280
杉並区 273,057 296,075
豊島区 145,334 144,174
北 区 174,910 177,066
荒川区 107,283 108,683
板橋区 278,662 288,228
練馬区 356,279 376,154
足立区 345,291 343,221
葛飾区 231,272 231,319
江戸川区 351,914 346,117
八王子市 281,506 280,954
立川市 91,460 92,362
武蔵野市 70,120 76,279
三鷹市 91,624 95,575
青梅市 67,393 66,693
府中市 130,582 129,429
昭島市 56,384 56,831
... ... ...
小金井市 59,955 61,488
小平市 95,312 98,284
日野市 92,983 92,410
東村山市 73,621 77,168
国分寺市 60,901 62,788
国立市 37,161 38,877
福生市 29,132 29,111
狛江市 40,005 42,476
東大和市 42,208 43,357
清瀬市 36,092 38,645
東久留米市 57,066 59,830
武蔵村山市 36,177 36,369
多摩市 72,927 75,818
稲城市 45,589 44,996
羽村市 28,251 27,356
あきる野市 40,304 40,547
西東京市 98,839 103,978
瑞穂町 16,922 16,291
日の出町 8,224 8,508
檜原村 1,100 1,117
奥多摩町 2,601 2,578
大島町 3,971 3,745
利島村 175 148
新島村 1,325 1,397
神津島村 975 923
三宅村 1,356 1,125
御蔵島村 167 150
八丈町 3,720 3,745
青ヶ島村 92 67
小笠原村 1,451 1,174
[62 rows x 2 columns]
ここで population.csv には下のデータが入っている。
市区町村,世帯数,総数,男,女,人口密度
千代田区,"35,830","63,635","31,935","31,700","5,458"
中央区,"91,852","162,502","77,241","85,261","15,916"
港 区,"145,865","257,426","121,326","136,100","12,638"
新宿区,"219,639","346,162","173,743","172,419","18,999"
文京区,"121,128","221,489","105,462","116,027","19,618"
台東区,"118,858","199,292","101,917","97,375","19,712"
墨田区,"150,855","271,859","134,678","137,181","19,743"
江東区,"267,262","518,479","256,116","262,363","12,910"
品川区,"220,678","394,700","193,644","201,056","17,281"
目黒区,"156,583","279,342","132,206","147,136","19,042"
大田区,"391,146","729,534","362,653","366,881","11,993"
世田谷区,"479,792","908,907","431,026","477,881","15,657"
渋谷区,"137,582","226,594","108,768","117,826","14,996"
中野区,"204,613","331,658","167,378","164,280","21,274"
杉並区,"321,531","569,132","273,057","296,075","16,710"
豊島区 ,"179,880","289,508","145,334","144,174","22,253"
北 区,"196,580","351,976","174,910","177,066","17,078"
荒川区,"115,944","215,966","107,283","108,683","21,256"
板橋区,"309,133","566,890","278,662","288,228","17,594"
練馬区,"370,567","732,433","356,279","376,154","15,234"
足立区,"346,739","688,512","345,291","343,221","12,930"
葛飾区,"233,158","462,591","231,272","231,319","13,293"
江戸川区,"342,016","698,031","351,914","346,117","13,989"
八王子市,"267,736","562,460","281,506","280,954","3,018"
立川市,"91,270","183,822","91,460","92,362","7,546"
武蔵野市,"76,765","146,399","70,120","76,279","13,333"
三鷹市,"93,665","187,199","91,624","95,575","11,401"
青梅市,"63,142","134,086","67,393","66,693","1,298"
府中市,"125,060","260,011","130,582","129,429","8,835"
昭島市,"53,827","113,215","56,384","56,831","6,529"
調布市,"118,804","235,169","114,909","120,260","10,898"
町田市,"195,643","428,685","209,971","218,714","5,991"
小金井市,"60,367","121,443","59,955","61,488","10,747"
小平市,"91,602","193,596","95,312","98,284","9,439"
日野市,"88,402","185,393","92,983","92,410","6,729"
東村山市,"72,676","150,789","73,621","77,168","8,797"
国分寺市,"60,111","123,689","60,901","62,788","10,793"
国立市,"37,728","76,038","37,161","38,877","9,330"
福生市,"30,506","58,243","29,132","29,111","5,733"
狛江市,"42,157","82,481","40,005","42,476","12,908"
東大和市,"38,852","85,565","42,208","43,357","6,376"
清瀬市,"35,454","74,737","36,092","38,645","7,306"
東久留米市,"54,257","116,896","57,066","59,830","9,076"
武蔵村山市,"31,640","72,546","36,177","36,369","4,735"
多摩市,"71,851","148,745","72,927","75,818","7,080"
稲城市,"39,991","90,585","45,589","44,996","5,041"
羽村市,"25,718","55,607","28,251","27,356","5,617"
あきる野市,"35,519","80,851","40,304","40,547","1,100"
西東京市,"97,350","202,817","98,839","103,978","12,877"
瑞穂町,"14,912","33,213","16,922","16,291","1,971"
日の出町,"7,383","16,732","8,224","8,508",596
檜原村,"1,181","2,217","1,100","1,117",21
奥多摩町,"2,685","5,179","2,601","2,578",23
大島町,"4,635","7,716","3,971","3,745",85
利島村,174,323,175,148,78
新島村,"1,381","2,722","1,325","1,397",99
神津島村,917,"1,898",975,923,102
三宅村,"1,620","2,481","1,356","1,125",45
御蔵島村,170,317,167,150,15
八丈町,"4,365","7,465","3,720","3,745",103
青ヶ島村,109,159,92,67,27
小笠原村,"1,492","2,625","1,451","1,174",25
引用：住民基本台帳による東京都の世帯と人口（町丁別・年齢別）
pandas の read_csv はファイルの内容を DataFrame にする。読み込んだ DataFrame にカラム名を入れると、そのカラムに属する値だけが返る。
1 つの列のみを選択する
pandas を使って population.csv から各自治体の人口総数のみを選択してみよう。
import pandas as pd
df = pd.read_csv('population.csv', index_col=0)
rows = df['総数']
print(rows)
print(type(rows))
今回は 1 つの列「総数」のみを選択している。結果はこうなる。
市区町村
千代田区 63,635
中央区 162,502
港 区 257,426
新宿区 346,162
文京区 221,489
台東区 199,292
墨田区 271,859
江東区 518,479
品川区 394,700
目黒区 279,342
大田区 729,534
世田谷区 908,907
渋谷区 226,594
中野区 331,658
杉並区 569,132
豊島区 289,508
北 区 351,976
荒川区 215,966
板橋区 566,890
練馬区 732,433
足立区 688,512
葛飾区 462,591
江戸川区 698,031
八王子市 562,460
立川市 183,822
武蔵野市 146,399
三鷹市 187,199
青梅市 134,086
府中市 260,011
昭島市 113,215
...
小金井市 121,443
小平市 193,596
日野市 185,393
東村山市 150,789
国分寺市 123,689
国立市 76,038
福生市 58,243
狛江市 82,481
東大和市 85,565
清瀬市 74,737
東久留米市 116,896
武蔵村山市 72,546
多摩市 148,745
稲城市 90,585
羽村市 55,607
あきる野市 80,851
西東京市 202,817
瑞穂町 33,213
日の出町 16,732
檜原村 2,217
奥多摩町 5,179
大島町 7,716
利島村 323
新島村 2,722
神津島村 1,898
三宅村 2,481
御蔵島村 317
八丈町 7,465
青ヶ島村 159
小笠原村 2,625
Name: 総数, Length: 62, dtype: object
<class 'pandas.core.series.Series'>
市区町村名が出力されているが rows は一次元のデータである。このデータは pandas の Series という型で、純粋な Python の list に相当する。もちろん Series と list は違う。
pandas の Series は最大値、最小値といった標準的な関数を最初から用意している。次の記事では人口の最大値、最小値、分散などを求める。
pandas
