[R] Help needed for efficient way to loop through rows and columns

[David L Carlson]

Can you show us what you want the final data.frame to look like? You've
created five variables stored as factors and you seem to be trying to change
those to numeric values? Is that correct? 

Since AB and BA are always set to 1, you could just replace those values
globally rather than mess with the ifelse commands for those values. Only AA
and BB are affected by the value of AorB.

Your apply() function processes the data.frame by row so i is a vector
consisting of all the values in the row. You seem to be coding as if i was a
single integer (as in a for loop).

----------------------------------------------
David L Carlson
Associate Professor of Anthropology
Texas A&M University
College Station, TX 77843-4352


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Priya Bhatt
> Sent: Wednesday, May 16, 2012 3:08 AM
> To: r-help at r-project.org
> Subject: [R] Help needed for efficient way to loop through rows and
> columns
> 
> Dear R-helpers:
> 
> I am trying to write a script that iterates through a dataframe that
> looks
> like this:
> 
> 
> Example dataset called "sample":
> 
> names <- c("S1", "S2", "S3", "S4")
> X <- c("BB", "AB", "AB", "AA")
> Y <- c("BB", "BB", "AB", "AA")
> Z <- c("BB", "BB", "AB", NA)
> AorB <- c("A", "A", "A", "B")
> 
> sample <- data.frame(names, X, Y, Z, AorB)
> 
> 
> for a given row,
> 
> if AorB == A, then AA == 2, AB = 1, BA = 1, BB = 0
> 
> if AorB == B, then AA == 0, AB = 1, BA = 1, BB = 2
> 
> I've been trying  to write this using apply and ifelse statements in
> hopes
> that my code runs quickly, but I'm afraid I've make a big mess.  See
> below:
> 
> apply(sample, 1, function(i) {
> 
> 
>   ifelse(sample$AorB[i] == "A",
>          (ifelse(sample[i,] == "AA", sample[i,] <- 2 ,
>                  ifelse(sample[i,] == "AB" || sample[i,] == "BA" ,
> sample[i,] <- 1,
>                         ifelse(sample[i,] == "BB", sample[i,] <- 0,
> sample[i,] <- NA )) )
>           )   , ifelse(sample$AorB[i,] == "B"),
>          (ifelse(sample[i,] == "AA", sample[i,] <- 0 ,
>                  ifelse(sample[i,] == "AB" || sample[i,] == "BA" ,
> sample[i,] <- 1,
>                         ifelse(sample[i,] == "BB", sample[i,] <- 2,
> sample[i,] <- NA))))) })
> 
> 
> Any Advice?
> 
> 	[[alternative HTML version deleted]]
> 
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