Question

我有一个带有列标题的data.frame。

如何从data.frame中获取特定行作为列表（列标题为列表的键）？

具体来说，我的data.frame是

      A    B    C
    1 5    4.25 4.5
    2 3.5  4    2.5
    3 3.25 4    4
    4 4.25 4.5  2.25
    5 1.5  4.5  3

我希望得到一个相当于

的行

> c(a=5, b=4.25, c=4.5)
  a   b   c 
5.0 4.25 4.5

Answer 1

x[r,]

其中r是您感兴趣的行。请尝试此操作，例如：

#Add your data
x <- structure(list(A = c(5,    3.5, 3.25, 4.25,  1.5 ), 
                    B = c(4.25, 4,   4,    4.5,   4.5 ),
                    C = c(4.5,  2.5, 4,    2.25,  3   )
               ),
               .Names    = c("A", "B", "C"),
               class     = "data.frame",
               row.names = c(NA, -5L)
     )

#The vector your result should match
y<-c(A=5, B=4.25, C=4.5)

#Test that the items in the row match the vector you wanted
x[1,]==y

This page（来自this useful site）提供了有关索引的良好信息。

Answer 2

逻辑索引非常R-ish。试试：

 x[ x$A ==5 & x$B==4.25 & x$C==4.5 , ]

或者：

subset( x, A ==5 & B==4.25 & C==4.5 )

Answer 3

尝试：

> d <- data.frame(a=1:3, b=4:6, c=7:9)

> d
  a b c
1 1 4 7
2 2 5 8
3 3 6 9

> d[1, ]
  a b c
1 1 4 7

> d[1, ]['a']
  a
1 1

Answer 4

如果您不知道行号，但知道某些值，则可以使用子集

x <- structure(list(A = c(5,    3.5, 3.25, 4.25,  1.5 ), 
                    B = c(4.25, 4,   4,    4.5,   4.5 ),
                    C = c(4.5,  2.5, 4,    2.25,  3   )
               ),
               .Names    = c("A", "B", "C"),
               class     = "data.frame",
               row.names = c(NA, -5L)
     )

subset(x, A ==5 & B==4.25 & C==4.5)

Answer 5

10年后--->使用tidyverse，我们可以简单地实现这一点，并从Christopher Bottoms借用叶子。为了更好地掌握，请参阅slice()。

library(tidyverse)
x <- structure(list(A = c(5,    3.5, 3.25, 4.25,  1.5 ), 
                    B = c(4.25, 4,   4,    4.5,   4.5 ),
                    C = c(4.5,  2.5, 4,    2.25,  3   )
),
.Names    = c("A", "B", "C"),
class     = "data.frame",
row.names = c(NA, -5L)
)

x
#>      A    B    C
#> 1 5.00 4.25 4.50
#> 2 3.50 4.00 2.50
#> 3 3.25 4.00 4.00
#> 4 4.25 4.50 2.25
#> 5 1.50 4.50 3.00

y<-c(A=5, B=4.25, C=4.5)
y
#>    A    B    C 
#> 5.00 4.25 4.50

#The slice() verb allows one to subset data row-wise. 
x <- x %>% slice(1) #(n) for the nth row, or (i:n) for range i to n, (i:n()) for i to last row...

x
#>   A    B   C
#> 1 5 4.25 4.5

#Test that the items in the row match the vector you wanted
x[1,]==y
#>      A    B    C
#> 1 TRUE TRUE TRUE

^{由reprex package（v0.3.0）于2020-08-06创建}

如何从R data.frame获取行

5 个答案: