我认为我没有在标题中明确说明，所以我只是说明了问题： assdt是一个载体：
assdt
[1] 18 19 1 0 33 26 3 2 31 42 43 41 44
dt是一个矩阵：
dt 0 dt 1 dt 2 dt 3 dt 4 dt 5 dt 6 dt 7 dt 8 dt 9 dt 10 dt 11 dt 12 dt 13 dt 14 dt 15 dt 16 dt 17 dt 18 dt 19 dt 20
[1,] "0" "0" "0" "1" "0" "1" "0" "0" "0" "0" "0" "0" "1" "0" "1" "0" "0" "0" "0" "0" "0"
[2,] "0" "0" "0" "1" "0" "1" "0" "1" "0" "0" "0" "0" "0" "0" "1" "0" "0" "0" "0" "0" "0"
[3,] "0" "0" "0" "1" "0" "0" "0" "1" "0" "0" "0" "0" "0" "0" "1" "0" "0" "0" "0" "0" "0"
[4,] "0" "0" "0" "1" "0" "0" "0" "1" "0" "0" "0" "0" "0" "0" "1" "0" "0" "0" "0" "0" "0"
[5,] "0" "0" "0" "1" "0" "0" "0" "0" "0" "0" "0" "0" "0" "0" "1" "0" "0" "0" "0" "0" "0"
[6,] "0" "0" "0" "1" "0" "0" "1" "0" "1" "0" "0" "0" "0" "0" "1" "0" "0" "0" "0" "0" "0"
dt 21 dt 22 dt 23 dt 24 dt 25 dt 26 dt 27 dt 28 dt 29 dt 30 dt 31 dt 32 dt 33 dt 34 dt 35 dt 36 dt 37 dt 38 dt 39
[1,] "0" "0" "0" "0" "0" "0" "1" "1" "0" "0" "0" "0" "0" "0" "0" "0" "1" "1" "0"
[2,] "0" "0" "0" "0" "0" "0" "1" "1" "0" "0" "0" "0" "0" "0" "0" "0" "1" "1" "0"
[3,] "0" "0" "0" "0" "0" "0" "1" "1" "0" "0" "0" "0" "0" "0" "0" "0" "1" "1" "0"
[4,] "0" "0" "0" "0" "0" "0" "1" "1" "0" "0" "0" "0" "0" "0" "0" "0" "1" "1" "0"
[5,] "0" "0" "0" "0" "0" "0" "1" "1" "0" "0" "0" "0" "0" "0" "0" "0" "1" "1" "0"
[6,] "0" "0" "0" "0" "0" "0" "1" "1" "0" "0" "0" "0" "0" "0" "0" "0" "1" "1" "0"
dt 40
[1,] "1"
[2,] "1"
[3,] "1"
[4,] "1"
[5,] "1"
[6,] "1"
我想选择selectdt <- c(18,19,1,0,33,26,3,2,31,42,43,41,44)中的列。 dt中没有第42,43,44列，所以只是忽略它们，我做dt[,selectdt]时出现错误subscript out of bounds。怎么做？
答案 0 :(得分：1)
mat <- as.matrix(mtcars)
cols <- c(1,5,20)
mat[, cols]
#Error in mat[, cols] : subscript out of bounds
mat[, cols[cols <= ncol(mat)]]
# mpg drat
#Mazda RX4 21.0 3.90
#Mazda RX4 Wag 21.0 3.90
#...