On Aug 31, 2015, at 1:49 PM, Luigi Marongiu wrote:
> Dear all,
> I have a data frame and I would like to do the following:
> a) replace value of one variable "a" according to the value of another one "b"
> b) remove all the instances of the variable "b"
>
> For the sake of argument, let's say I have the following data frame:
> test <- rep(c("Adenovirus", "Rotavirus", "Norovirus", "Rotarix",
> "Sapovirus"), 3)
> res <- c(0, 1, 0, 0, 1,
> 1, 0, 1, 1, 0,
> 0, 1, 0, 1, 0)
> samp <- c(rep(1, 5), rep(2, 5), rep(3, 5))
> df <- data.frame(test, res, samp, stringsAsFactors = FALSE)
>
> The task I need is to coerce the results of the "Rotavirus" to
> negative (0) if and only if "Rotarix" is positive (1). In this
> example, the results shows that for "samp" 3 "Rotavirus" should be 0:
> test res samp
> 2 Rotavirus 1 1
> 4 Rotarix 0 1
> 7 Rotavirus 0 2
> 9 Rotarix 1 2
> 12 Rotavirus 1 3
> 14 Rotarix 1 3
>
> I can't use the subset function because then I would work on a
> separate object and I don't know how to implement the conditions for
> the replacements.
> Finally, all the "Rotarix" entries should be removed from the data frame.
>From context it appears you want to do this testing within groups determined
>by 'samp', so you might choose to use an lapply-split approach:
lapply( split(df, df$samp),
FUN=function(d) if ( d[d$test =="Rotarix", "res"] ) {
d$res[d$test=="Rotavirus"] <- 0 ; return( d[!d$test=="Rotarix", ] ) } else {
d[!d$test=="Rotarix", ]} )
$`1`
test res samp
1 Adenovirus 0 1
2 Rotavirus 1 1
3 Norovirus 0 1
5 Sapovirus 1 1
$`2`
test res samp
6 Adenovirus 1 2
7 Rotavirus 0 2
8 Norovirus 1 2
10 Sapovirus 0 2
$`3`
test res samp
11 Adenovirus 0 3
12 Rotavirus 0 3
13 Norovirus 0 3
15 Sapovirus 0 3
It's pretty easy to rbind.data.frame those together
> do.call( rbind.data.frame, lapply( split(df, df$samp), FUN=function(d) if (
> d[d$test =="Rotarix", "res"] ) { d$res[d$test=="Rotavirus"] <- 0 ; return(
> d[!d$test=="Rotarix", ] ) } else { d[!d$test=="Rotarix", ]} ) )
test res samp
1.1 Adenovirus 0 1
1.2 Rotavirus 1 1
1.3 Norovirus 0 1
1.5 Sapovirus 1 1
2.6 Adenovirus 1 2
2.7 Rotavirus 0 2
2.8 Norovirus 1 2
2.10 Sapovirus 0 2
3.11 Adenovirus 0 3
3.12 Rotavirus 0 3
3.13 Norovirus 0 3
3.15 Sapovirus 0 3
> Thank you.
> Best regards,
> Luigi
>
> ______________________________________________
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David Winsemius
Alameda, CA, USA
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