Extract positions with values higher than 10 from certain rows and columns in a dataframe-CodePudding

I want to extract the positions which are higher than 10 from row 3,6,9 and column 2,3. Any suggestions of how to do this? Many thanks!

df <- data.frame(a=c(1,3,99,45,67,5,34,1,6), b=c(45,8,79,3,12,76,9,10,87),c=c(46,7,21,9,89,34,1,67,56),d=c(56,1,1,76,42,78,98,4,8))

    
> df
   a  b  c  d
1  1 45 46 56
2  3  8  7  1
3 99 79 21  1
4 45  3  9 76
5 67 12 89 42
6  5 76 34 78
7 34  9  1 98
8  1 10 67  4
9  6 87 56  8

Wanted output:

      row column
[1,]   3      2
[2,]   3      3
[3,]   6      2
[4,]   6      3
[5,]   9      2
[6,]   9      3

CodePudding user response：

We may use which with arr.ind on a logical matrix to get the row/column indexes. Then subset the rows of the index matrix based on the values in the row/col values

ind <- which(df > 10, arr.ind = TRUE)
ind[ind[,1] %in% c(3, 6, 9) & ind[,2] %in% 2:3,]

-output

     row col
[1,]   3   2
[2,]   6   2
[3,]   9   2
[4,]   3   3
[5,]   6   3
[6,]   9   3