[R] Extracting Vectors from Lists of Lists Produced by Functions

[Sundar Dorai-Raj]

White, Charles E WRAIR-Wash DC wrote:
> If you found my subject heading to be confusing then I'm sure you'll enjoy
> the example I've included below. I find the apply type functions to be
> wonderful for avoiding loops but when I use them with existing functions, I
> end up using loops anyway to extract the vectors I want. I would appreciate
> it if someone could show me how to avoid these loops. Thanks.
> 
> EXAMPLE: 
> noise<-matrix(data = rnorm(15, mean=0, sd=1), nrow = 5, ncol = 3,
>               byrow = FALSE, dimnames = NULL)
> measure<-apply(noise,2,t.test)
> measure
> tval<-NULL
> df<-NULL
> pval<-NULL
> for (i in 1:length(measure)){
>   tval[i]<-measure[[i]][[1]]
>   df[i]<-measure[[i]][[2]]
>   pval[i]<-measure[[i]][[3]]}
> data.frame(tval,df,pval)
> 
> Charles E. White, Biostatistician
> Walter Reed Army Institute of Research
> 503 Robert Grant Ave., Room 1w102
> Silver Spring, MD 20910-1557
> 301 319-9781
> WRAIR Home Page: http://wrair-www.army.mil/
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> 

Charles,

Use a data.frame and sapply instead.

sapply(as.data.frame(noise), function(x) t.test(x)[1:3])

Sundar