r - 从数据框列表中提取观察值的索引列表

Question

我有一个索引列表，我想使用这些索引从数据框列表中提取观察结果。一个简化的例子如下:

#A list of indices used to extract observations based on the time column from the `dat` dataset
time.index <- list(c(1,2,3), c(4,5,6), c(2,3,4))
#A list of data frames in which observations will be extracted based on the time column 
dat <- list(case1=data.frame(time=1:10, y=rnorm(10)), case2=data.frame(time=1:10, y=rnorm(10)), case3=data.frame(time=1:10, y=rnorm(10)))
#The expected result will be like this:
$case1
   time          y
1     1 -0.8954070
2     2  0.0270242
3     3 -0.4256890

$case2
   time       y
4     4  1.5789
5     5 -0.6692
6     6 -2.3306

$case3
   time       y
2     2 -0.7371
3     3 -0.3271
4     4  0.4128

谁知道如何实现？非常感谢!

Answer 1

你可以使用 map :

Map(function(x, y) x[x$time %in% y, ], dat, time.index)

#$case1
#  time     y
#1    1  1.75
#2    2  1.13
#3    3 -1.45

#$case2
#  time     y
#4    4 2.212
#5    5 0.572
#6    6 0.149

#$case3
#  time       y
#2    2 -0.0377
#3    3 -0.1700
#4    4  0.8414

类似地，使用 purrr 的 map2 :

purrr::map2(dat, time.index, ~.x[.x$time %in% .y, ])