Question

一些问题，R语言可能有优雅的解决方案......

给定，矩阵m包含二进制值1和0，以及列索引的向量v

我如何编写一个函数来提取m中的所有行由v？
作为一个额外的功能，如何返回行索引相应的行？

如果我用一个例子来说明，那可能是最好的......

假设我要求的逻辑驻留在函数selectByIndices（matrix，indexVector）中。

所以如果我们有矩阵（或者可能是等效的数据帧）：

 >(m= matrix(c( 1, 0, 1, 1, 1,0, 1, 1, 0, 1,1, 0, 1, 1, 0,1, 1, 1, 
   0, 1,0, 1, 0, 0, 1), 5))

         [,1] [,2] [,3] [,4] [,5]
  [1,]    1    0    1    1    0
  [2,]    0    1    0    1    1
  [3,]    1    1    1    1    0
  [4,]    1    0    1    0    0
  [5,]    1    1    0    1    1

和索引向量：

 >c1 = c(1,3,4)
 >c2 =  c(4,5)
 >c3 =  c(1,3,5)

该函数的行为类似于：

 >selectByIndices( m, c1)

        [,1] [,2] [,3] [,4] [,5]
  [1,]    1    0    1    1    0
  [3,]    1    1    1    1    0


 >selectByIndices( m, c2)

        [,1] [,2] [,3] [,4] [,5]
  [2,]    0    1    0    1    1
  [5,]    1    1    0    1    1


 >selectByIndices( m, c3)

    #no rows (i.e. empty collection) returned

希望它足够清楚，先谢谢你的帮助。

Answer 1

## Create a function that extracts the qualifying rows
f <- function(m, j) {
    m[rowSums(m[, j]) == length(j),]
    # m[apply(m[, j], 1, function(X) all(X==1)),] ## This would also work
    # which(rowSums(m[, j]) == length(j))         ## & this would get row indices
}

## Try it out
f(m, c1)
#      [,1] [,2] [,3] [,4] [,5]
# [1,]    1    0    1    1    0
# [2,]    1    1    1    1    0

f(m, c2)
#      [,1] [,2] [,3] [,4] [,5]
# [1,]    0    1    0    1    1
# [2,]    1    1    0    1    1

Answer 2

> selectRows <- function(mat, rown) suppressWarnings(mat[apply( mat[, rown], 1, all) , ])
> selectRows(m, c1)
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    0    1    1    0
[2,]    1    1    1    1    0

>  whichRows <-function(mat, rown) suppressWarnings( which( apply( mat[, rown], 1, all) ) )
> whichRows(m, c1)
[1] 1 3

从具有动态列索引的二进制矩阵中选择子集

2 个答案: