CODEWITHSUNDEEP
rmath
Johnathan
Johnathan

Reputation: 1907

How to perform a subtract across only one column of a matrix?

I have a large character matrix:

Chromosome   Start    End   ... 
1            1        5000  ...
2            1        4000  ...
...          ...      ...

I would like to subtract 1 from each entry of the second column. The first idea that comes to mind is to separate each column, convert the second as numeric, perform the subtraction and use cbind to patch everything together. However, since I have over 20 columns, I want something more efficient.

I would appreciate your input.

Thank you!

Upvotes: 1

Views: 213

Answers (2)

IRTFM
IRTFM

Reputation: 263311

Why not just (now assuming character matrix but would also work w/ datafreme.)

dat[ ,2 ] <- as.numeric(dat[, 2 ])-1

Upvotes: 2

David Arenburg
David Arenburg

Reputation: 92282

I would recommend gsubfn package as it is designed especially for cases like that, in particular:

library(gsubfn)
dat[, 2] <- gsubfn("\\d", function(x) as.numeric(x) - 1, dat[, 2])
dat
##      Chromosome Start End   
## [1,] "1"        "0"   "5000"
## [2,] "2"        "0"   "4000"

Upvotes: 0

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