Select row by its list index in r-CodePudding

I would like to extract the row by its list index. I tried to search in stackoverflow but most of the solution only works for certain index (e.g. sapply(list,"[[,1) (This select every first row) or sapply(list,"[,1:2) (This select every first and second rows)).

Here is an example:

set.seed(123)
x<-data.frame(matrix(runif(9),ncol=3))
y<-data.frame(matrix(runif(9),ncol=3))
z<-data.frame(matrix(runif(9),ncol=3))

lst<-list(x,y,z)

lst
[[1]]
         X1        X2        X3
1 0.2875775 0.8830174 0.5281055
2 0.7883051 0.9404673 0.8924190
3 0.4089769 0.0455565 0.5514350

[[2]]
         X1        X2         X3
1 0.4566147 0.6775706 0.89982497
2 0.9568333 0.5726334 0.24608773
3 0.4533342 0.1029247 0.04205953

[[3]]
         X1        X2        X3
1 0.3279207 0.6928034 0.6557058
2 0.9545036 0.6405068 0.7085305
3 0.8895393 0.9942698 0.5440660

Desired output:

lst
[[1]] #select first row
         X1        X2        X3
1 0.2875775 0.8830174 0.5281055

[[2]] #select second row
         X1        X2         X3
1 0.9568333 0.5726334 0.24608773

[[3]] #select third row
         X1        X2        X3
1 0.8895393 0.9942698 0.5440660

CodePudding user response：

We may use imap. As the list is unnamed, the .y will be the sequence index of the list, which we used in slice to subset the rows

library(purrr)
library(dplyr)
imap(lst, ~ .x %>%
     slice(.y))

-output

[[1]]
         X1        X2        X3
1 0.2875775 0.8830174 0.5281055

[[2]]
         X1        X2        X3
1 0.9568333 0.5726334 0.2460877

[[3]]
         X1        X2       X3
1 0.8895393 0.9942698 0.544066

Or using base R with Map

Map(function(x, i) x[i,], lst, seq_along(lst))

-output

[[1]]
         X1        X2        X3
1 0.2875775 0.8830174 0.5281055

[[2]]
         X1        X2        X3
2 0.9568333 0.5726334 0.2460877

[[3]]
         X1        X2       X3
3 0.8895393 0.9942698 0.544066