根据向量选择矩阵列答案

【问题标题】：Select column of matrix based on a vetcor根据向量选择矩阵列
【发布时间】：2014-08-22 14:57:32
【问题描述】：

我不认为我在标题中描述得很清楚，所以我只是显示问题： assdt 是一个向量：

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，所以忽略它们，我做了dt[,selectdt] 有一个错误subscript out of bounds。怎么做？

【问题讨论】：

dt[,selectdt[selectdt
如果selectdt 中也可能有负值，您可以使用dt[, intersect(selectdt, seq_len(ncol(dt)))]

标签： r matrix vector

【解决方案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
#...

【讨论】：