列の選択

Julia でのデータ操作

Katerina Zahradova

Instructor

米国の最低賃金

# wages を表示
wages

2703×10 DataFrame 2678 rows omitted 5 columns omitted
Row  year   state     region   state_min_wage    state_min_wage_2020_dollars ...
     Int64  String31  String3  Float64           Float64           ...
______________________________________________________________________________
1    1968   Alabama   S        0.0               0.0               ...
2    1968   Alaska    W        2.1               15.61             ...
...

スライス方法

# 列番号で選択
wages[:, 1]

# 列名で選択
wages[:, "year"]
wages[:, :year]

# 列名で選択
wages.year

# 複数列を選択
wages[:, ["year", "state"]]
wages[:, [:year, :state]]
wages[:, [1,2]]

列の選択

# 州、年、州の最低賃金を選択

select(wages, 2, 1, 4)

2703×3 DataFrame 2678 rows omitted
Row  state     year        state_min_wage    
     String31  Int64       Float64                      
____________________________________________
1    Alabama   1968        0.0                              
2    Alaska    1968        2.1                            
...

列の選択

# 州、年、州の最低賃金を選択
select(wages, "state", :year, 4)

2703×3 DataFrame 2678 rows
Row  state     year        state_min_wage    
     String31  Int64       Float64                      
____________________________________________
1    Alabama   1968        0.0                              
2    Alaska    1968        2.1                            
...

パターンで選択

列の選択

ある文字/語で始まる・終わる
部分文字列を含む
...

... 大規模データでは面倒

パターンで選択

# state で始まる全列
select(wages, Cols(startswith("state")))

2703×3 DataFrame 2702 rows omitted
Row state    state_min_wage state_min_wage_2020_dollars
    String31 Float64        Float64
__________________________________________
1   Alabama  0.0            0.0
...

パターンで選択

# 2020_dollars で終わる全列
select(wages, Cols(endswith("2020_dollars")))

2703x3 DataFrame 2702 rows omitted
Row state_min_wage_2020_dollars  federal_min_wage_2020_dollars  effective_min_wage_2020_dollars
    Float64                      Float64                        Float64
________________________________________________________________________________________________
1   0.0                          8.55                           8.55
...

パターンで選択

# min を含む全列
select(wages, Cols(contains.("min")))

2703×6 DataFrame 2702 rows omitted 3 columns omitted
Row  state_min_wage  state_min_wage_2020_dollars  federal_min_wage  ...    
     Float64         Float64                      Float64           ...
_______________________________________________________________________
1    0.0             0.0                          1.15              ...
...

正規表現

regex = regular expressions（正規表現）

文字列
複雑なパターンの照合・位置特定に有用
さらに学ぶ: DataCamp Cheat Sheet、regex101.com など

正規表現の使用

# 正規表現で選択
select(wages, r"min")

2703×6 DataFrame 2702 rows omitted 3 columns omitted
Row  state_min_wage  state_min_wage_2020_dollars  federal_min_wage  ...    
     Float64         Float64                      Float64           ...
_______________________________________________________________________
1    0.0             0.0                          1.15              ...
...

select!() と select() の違い

# 元のDataFrameを変更
select!(wages, :year, :state)

# 元のDataFrameが変化
println(first(wages))

DataFrameRow (2 columns)
Row  year    state     
     Int64   String31  
______________________
1    1968    Alabama

# 新しいDataFrameを返す
select(wages, :year, :state)

# 元のDataFrameはそのまま
println(first(wages))

DataFrameRow (10 columns, 7 omitted)
Row  year    state     region    ...
     Int64   String31  String3   ...
____________________________________
1    1968    Alabama   S         ...

Ayo berlatih!

Julia でのデータ操作