CODEWITHSUNDEEP
r
StudentOfScience
StudentOfScience

Reputation: 809

R: Getting rows from specific columns

In R, say you have a named numeric such as:

3777 3727 3421 2373 3259  512 3174 3456 3536  805 
   4    4    8    9    2    2    6    4    6    6

The values on the top are rownames from a larger matrix, and the values below it are the column of data I want from that row.

So, I want from dataframe (or matrix) row with name 3777, col 4's value. and so on.

What is the easiest way to do this?

thank you.

Upvotes: 2

Views: 69

Answers (2)

CT Zhu
CT Zhu

Reputation: 54340

Can you use row index instead of row names? If so, you don't need a loop:

a <- rnorm(10000)
M <- matrix(a,nrow=100)
c1 <- c(1,3,4,5,9) #3777 3727 3421 2373 3259  512 3174 3456 3536  805
c2 <- c(3,8,10,11,23)  #   4    4    8    9    2    2    6    4    6    6
M[cbind(c1,c2)]
# [1] -0.8216866  0.5427404  0.4462874 -0.6547175 -1.6598367

Upvotes: 2

StudentOfScience
StudentOfScience

Reputation: 809

The way I did it is:

myMatrix #any matrix

myNamedNum #from above example

for (i in 1:length(myNamedNum)){

    myMatrix[names(myNamedNum[i]),as.numeric(myNamedNum[i])]
}

Upvotes: 0

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