我正在尝试使用R来列出列表中的行数。
我有2个列表，一个包含n行和p列的矩阵，第二个列表包含我需要子集的行数。
mat <- list(a = matrix(rnorm(8*4),8), b = matrix(rnorm(15*4),15), c = matrix(rnorm(7*4),7))
rw <- list(a = 6, b = 7, c = 4)
两个列表都有通用名称，在上面的例子中，我想保留元素前6行，b前7行和c 4行。
你会如何在R
答案 0 :(得分：4)
Map的一个解决方案：
Map(function(x, y) x[1:y, ], mat, rw)
# $a
# [,1] [,2] [,3] [,4]
# [1,] 1.3331549 -0.6985623 -1.1842788 -0.1496880
# [2,] 0.2096395 -0.2901906 0.4210395 0.9116542
# [3,] 0.1763317 1.3858205 -1.1567526 -1.1794618
# [4,] 1.3596395 0.5815012 -0.3681799 -0.6569447
# [5,] 0.2251352 0.2331387 -1.2509844 -1.1346729
# [6,] 0.6796729 1.1274772 0.3992489 0.2305927
#
# $b
# [,1] [,2] [,3] [,4]
# [1,] 0.30700748 -1.2173855 -0.3377885 -0.6748974
# [2,] 1.09506443 -0.6142685 -1.1301122 -0.7792081
# [3,] -0.61049306 -1.3414474 0.9771373 1.0191636
# [4,] 0.66687294 -0.5269721 0.9971987 -0.6514121
# [5,] 0.54623236 0.9020964 0.3252700 -0.3925129
# [6,] -0.04848903 -0.5204047 0.3344675 -0.3232105
# [7,] -0.56502719 -0.3743275 2.1760364 -0.2941956
#
# $c
# [,1] [,2] [,3] [,4]
# [1,] -0.3225609 -0.40126955 -1.787255 -1.5005721
# [2,] 0.3474430 -1.16657015 1.106033 0.3114282
# [3,] 0.4099467 -0.04353555 0.838330 0.3282246
# [4,] -1.4648740 0.51279791 0.198768 -0.3394502