pandasのdataframeに列を追加する方法
column名指定して追加する場合
df[追加column名] = 追加データinsertを使う場合
df.insert(追加する位置,追加column名,追加データ)assignを使う場合
df = df.assign(追加column名 = 追加データ)column名を指定して追加
最終列に追加される
import pandas as pd
import numpy as np
# DataFrame作成
df = pd.DataFrame([[25,'pika','Electric',np.NaN],
[131,'rara','Water','Ice'],
[143,'gon','Normal',np.NaN],
[3,'fushi','Grass','Poison'],
[6,'kage','Fire','Flying'],
[9,'kame','Water',np.NaN]],
columns=['no','name','type1','type2'],
index=['party1','party2','party3','party4','party5','party6'])
# 作成したDataFrameの確認
print(df)
"""
no name type1 type2
party1 25 pika Electric NaN
party2 131 rara Water Ice
party3 143 gon Normal NaN
party4 3 fushi Grass Poison
party5 6 kage Fire Flying
party6 9 kame Water NaN
"""
# [level]という名前のカラム（列）追加
df['level'] = [88,80,82,84,84,84]
# 追加後確認
print(df)
"""
no name type1 type2 level
party1 25 pika Electric NaN 88
party2 131 rara Water Ice 80
party3 143 gon Normal NaN 82
party4 3 fushi Grass Poison 84
party5 6 kage Fire Flying 84
party6 9 kame Water NaN 84
"""追加するデータをリストではなく1つのデータを指定することですべての行に同じデータが入る
# 上記に加えて
# [itemheld]という名前のカラム（列）追加
df['itemheld'] = np.NaN
# 追加後確認
print(df)
"""
no name type1 type2 level helditem
party1 25 pika Electric NaN 88 NaN
party2 131 rara Water Ice 80 NaN
party3 143 gon Normal NaN 82 NaN
party4 3 fushi Grass Poison 84 NaN
party5 6 kage Fire Flying 84 NaN
party6 9 kame Water NaN 84 NaN
"""insertを使う
insertを使うと任意の場所（列）に追加することが可能
import pandas as pd
import numpy as np
# DataFrame作成
df = pd.DataFrame([[25,'pika','Electric',np.NaN],
[131,'rara','Water','Ice'],
[143,'gon','Normal',np.NaN],
[3,'fushi','Grass','Poison'],
[6,'kage','Fire','Flying'],
[9,'kame','Water',np.NaN]],
columns=['no','name','type1','type2'],
index=['party1','party2','party3','party4','party5','party6'])
# 作成したDataFrameの確認
print(df)
"""
no name type1 type2
party1 25 pika Electric NaN
party2 131 rara Water Ice
party3 143 gon Normal NaN
party4 3 fushi Grass Poison
party5 6 kage Fire Flying
party6 9 kame Water NaN
"""
# [name]と[type1]の間に[level]列を追加
df.insert(2,'level',[88,80,82,84,84,84])
# 追加後確認
print(df)
"""
no name level type1 type2
party1 25 pika 88 Electric NaN
party2 131 rara 80 Water Ice
party3 143 gon 82 Normal NaN
party4 3 fushi 84 Grass Poison
party5 6 kage 84 Fire Flying
party6 9 kame 84 Water NaN
こちらも追加するデータをリストではなく1つのデータを指定することですべての行に同じデータが入る
# 上記に加えて
# [itemheld]という名前のカラム（列）を最後の列に追加
df.insert(len(df.columns),'itemheld',np.NaN)
# 追加後確認
print(df)
"""
no name level type1 type2 itemheld
party1 25 pika 88 Electric NaN NaN
party2 131 rara 80 Water Ice NaN
party3 143 gon 82 Normal NaN NaN
party4 3 fushi 84 Grass Poison NaN
party5 6 kage 84 Fire Flying NaN
party6 9 kame 84 Water NaN NaN
"""assignを使う
最終列に追加される。追加位置の指定ができない。lamda関数が使える。
追加のcolumn名は半角英数しか指定できない。（全角も設定できるかもしれないが方法をしらない）
import pandas as pd
import numpy as np
# DataFrame作成
df = pd.DataFrame([[25,'pika','Electric',np.NaN],
[131,'rara','Water','Ice'],
[143,'gon','Normal',np.NaN],
[3,'fushi','Grass','Poison'],
[6,'kage','Fire','Flying'],
[9,'kame','Water',np.NaN]],
columns=['no','name','type1','type2'],
index=['party1','party2','party3','party4','party5','party6'])
# 作成したDataFrameの確認
print(df)
"""
no name type1 type2
party1 25 pika Electric NaN
party2 131 rara Water Ice
party3 143 gon Normal NaN
party4 3 fushi Grass Poison
party5 6 kage Fire Flying
party6 9 kame Water NaN
"""
# [level]という名前のカラム（列）追加
df = df.assign(level = [88,80,82,84,84,84])
# 追加後確認
print(df)
"""
no name type1 type2 level
party1 25 pika Electric NaN 88
party2 131 rara Water Ice 80
party3 143 gon Normal NaN 82
party4 3 fushi Grass Poison 84
party5 6 kage Fire Flying 84
party6 9 kame Water NaN 84
"""くどいが追加するデータをリストではなく1つのデータを指定することですべての行に同じデータが入る
# 上記に加えて
# [itemheld]という名前のカラム（列）を最後の列に追加
df = df.assign(itemheld = np.NaN)
# 追加後確認
print(df)
"""
no name type1 type2 level helditem
party1 25 pika Electric NaN 88 NaN
party2 131 rara Water Ice 80 NaN
party3 143 gon Normal NaN 82 NaN
party4 3 fushi Grass Poison 84 NaN
party5 6 kage Fire Flying 84 NaN
party6 9 kame Water NaN 84 NaN
"""
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