根据另一列的相应行值创建行子集？

#让 CSV 包含两列“年龄”和“性别”，其中：

  Age = [30, 24, 55, 61, 70, 21]

  Gender = [Male, Female, Male, Male, Male, Female]

#我希望它向我显示与 Gender="Male" 相对应的所有 Age 值（以及值的数量）以及与 "Female" 相同的值

  using DataFrames

#所以这就是我尝试的

julia> df= CSV.read(raw"Clocation)", DataFrame)
julia> df. Age
6-element Vector{Int64}:
30
24
55
61
70
21

#针对示例进行调整

julia> df. Age, Gender
ERROR: UndefVarError: Gender not defined
Stacktrace:
 [1] top-level scope
   @ REPL[26]:1

#我想要的是“df.Age，Gender=Male”，但这也不起作用，我真的被困住了:( 来源：https://testdataframesjl.readthedocs.io/en/readthedocs/subsets/ https://testdataframesjl.readthedocs.io/en/readthedocs/subsets/

#有什么建议吗？先感谢您！ #Edit：所以我尝试

julia> combine(groupby(df, :Age), :Gender=>"Male")
200×2 DataFrame
 Row │ Age    Male
     │ Int64  String7
─────┼────────────────
   1 │    18  Male
   2 │    18  Male
   3 │    18  Male
   4 │    18  Female
   5 │    19  Male
   6 │    19  Male
   7 │    19  Male
   8 │    19  Female
   9 │    19  Male
  10 │    19  Female
  11 │    19  Male
  12 │    19  Male
  13 │    20  Female
  14 │    20  Male
  15 │    20  Female
  16 │    20  Male
  17 │    20  Male
  18 │    21  Male
  19 │    21  Female
  20 │    21  Female
  21 │    21  Female
  22 │    21  Female
  23 │    22  Female
  24 │    22  Male
  25 │    22  Female
  26 │    23  Female
  27 │    23  Female
  28 │    23  Female
  ⋮  │   ⋮       ⋮
 173 │    57  Male
 174 │    57  Female
 175 │    58  Female
 176 │    58  Male
 177 │    59  Male
 178 │    59  Male
 179 │    59  Male
 180 │    59  Male
 181 │    60  Male
 182 │    60  Female
 183 │    60  Female
 184 │    63  Male
 185 │    63  Female
 186 │    64  Male
 187 │    65  Female
 188 │    65  Male
 189 │    66  Female
 190 │    66  Male
 191 │    67  Male
 192 │    67  Female
 193 │    67  Male
 194 │    67  Male
 195 │    68  Female
 196 │    68  Female
 197 │    68  Male
 198 │    69  Male
 199 │    70  Male
 200 │    70  Male
      144 rows omitted

#现在我很困惑 来源：https://discourse.julialang.org/t/how-to-count-the-number-of-categories-present-in-a-column-of-a-dataframe/33244/3 https://discourse.julialang.org/t/how-to-count-the-number-of-categories-present-in-a-column-of-a-dataframe/33244/3

julia> df. Age, Gender

你在哪里看到这个语法？

这就是你想要的吗？：

julia> df = DataFrame(Age = [30, 24, 55, 61, 70, 21], Gender = ["Male", "Female", "Male", "Male", "Male", "Female"]);

julia> df[df.Gender .== "Male", :]
4×2 DataFrame
 Row │ Age    Gender 
     │ Int64  String 
─────┼───────────────
   1 │    30  Male
   2 │    55  Male
   3 │    61  Male
   4 │    70  Male

julia> df.Age[df.Gender .== "Male"]
4-element Vector{Int64}:
 30
 55
 61
 70