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revalpastena

Evaluating a combined string including NA

My aim is to code TRUE/FALSE evaluating a string generated from pasting three character cells. The following is what I have. 

cond.var<-"a"
relation<-"!="
cond.value<-"1"  
a<-1

as.numeric(eval(parse(text=paste(cond.var, relation, cond.value, sep=""))))

The above codes work when a number is stored in cond.value. The last line returns 0, which is correct. Yet, when NA is stored in cond.value (cond.value<-"NA"), the last line returns just NA, which is incorrect.

Any suggestion to fix this problem will be appreciated. Thanks.

Solution

  • Quite hackish but this would work without changing your setting (using magrittr-pipe to improve readability)

    library(magrittr)

paste("`", relation, "`(", cond.var, ", ", cond.value, ")", sep="") %>% 
    sub(paste0(cond.var, ", NA)"), paste0("is.na(", cond.var, "), TRUE)"), .) %>% 
    parse(text=.) %>% 
    eval() %>% 
    as.numeric()