[R] Make sure a data frame has been "fun through" a function

[Charles C. Berry]

On Tue, 21 Feb 2017, stephen sefick wrote:

> Sorry for not being clear. I have never used S3 methods before. Below is
> some R code that sketches out my idea. Is this a sensible solution?
>

Sure. See comments (untested) inline.

Chuck

> test_data <- data.frame(a=1:10, b=1:10, c=1:10)
>
> functionA <- function(x, impossible_genotype){
>    ##some data processing
>    y <- x
>
>    ##return S3 to be able to use impossible genotype later
>    class(y) <- append(class(y),"genotypes")

      class(y) <- c("genotypes",class(y))

>
>    attr(y, "impossible_genotype") <- impossible_genotype
>
>    return(y)
> }
>
> test_data_genotypes <- functionA(test_data, impossible_genotype="Ref")
>
> functionB <- function(x){
>    ##stop if pre-processed with functionA
>    if(sum(class(x)=="genotypes")!=1){stop("Need to pre-process data with
> functionA")}

     if(!(inherits("genotypes")){
 	stop("Need to pre-process data with functionA")}


or in functionA you could skip the class()<- and just set the
"impossible_genotypes" attribute to FALSE when there are none such.

Then here test

      if (is.null(attr(x,"impossible_genotypes"))){
 		stop("Need to pre-process data with functionA")
 	} else {
 		return(alleles)
 	}


>
>    ##use this later in functionB to
>    impossible_genotype <- attributes(x)$impossible_genotype

      impossible_genotype <- attr(x,"impossible_genotype")
>
>    alleles <- c("Ref", "Alt")
>
>    coded_genotype <- alleles[alleles!=impossible_genotype]

      maybe `!is.element(alleles,impossible_genotype)' is safer than `!='

>
>
>
>    return(coded_genotype)
> }
>
> ##stop if not pre-processed with functionA
> functionB(test_data)
>
> ##processed with functionA
> functionB(test_data_genotypes)
>