r - 在 R 中，如何按多列中的因素拆分/子集数据框？

Question

我的数据如下:

ID   Test Type       Subject  Marks
1    Unit test 1     English   85
2    Unit test 1     English   75
3    Unit test 1     English   78
1    Unit test 2     English   85
2    Unit test 2     English   75
3    Unit test 2     English   78
1    Unit test 1     Maths     78
2    Unit test 1     Maths     79
3    Unit test 1     Maths     98
1    Unit test 2     Maths     95
2    Unit test 2     Maths     98
3    Unit test 2     Maths     88

我想按“测试类型”和“主题”拆分数据。我应该使用什么函数？ 我想要的结果是:

data frame 1:
    ID   Test Type       Subject  Marks
    1    Unit test 1     English   85
    2    Unit test 1     English   75
    3    Unit test 1     English   78

data frame 2:
    ID   Test Type       Subject  Marks
    1    Unit test 2     English   85
    2    Unit test 2     English   75
    3    Unit test 2     English   78

data frame 3 :
    ID   Test Type       Subject  Marks
    1    Unit test 1     Maths     78
    2    Unit test 1     Maths     79
    3    Unit test 1     Maths     98

data frame 4:
    ID   Test Type       Subject  Marks
    1    Unit test 2     Maths     95
    2    Unit test 2     Maths     98
    3    Unit test 2     Maths     88

Answer 1

您可以使用split()(感谢 DrDom 的改进)。

split(df, list(df$Test.Type, df$Subject))
# $`Unit test 1.English`
#   ID   Test.Type Subject Marks
# 1  1 Unit test 1 English    85
# 2  2 Unit test 1 English    75
# 3  3 Unit test 1 English    78
# 
# $`Unit test 2.English`
#   ID   Test.Type Subject Marks
# 4  1 Unit test 2 English    85
# 5  2 Unit test 2 English    75
# 6  3 Unit test 2 English    78
# 
# $`Unit test 1.Maths`
#   ID   Test.Type Subject Marks
# 7  1 Unit test 1   Maths    78
# 8  2 Unit test 1   Maths    79
# 9  3 Unit test 1   Maths    98
# 
# $`Unit test 2.Maths`
#    ID   Test.Type Subject Marks
# 10  1 Unit test 2   Maths    95
# 11  2 Unit test 2   Maths    98
# 12  3 Unit test 2   Maths    88

其中df是原始数据。

df <- structure(list(ID = c(1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 
2L, 3L), Test.Type = structure(c(1L, 1L, 1L, 2L, 2L, 2L, 1L, 
1L, 1L, 2L, 2L, 2L), .Label = c("Unit test 1", "Unit test 2"), class = "factor"),
    Subject = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 
    2L, 2L, 2L), .Label = c("English", "Maths"), class = "factor"), 
    Marks = c(85L, 75L, 78L, 85L, 75L, 78L, 78L, 79L, 98L, 95L, 
    98L, 88L)), .Names = c("ID", "Test.Type", "Subject", "Marks"
), class = "data.frame", row.names = c(NA, -12L))