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Asked: 2026-06-05T20:57:55+00:00

So I’ve been trying to figure out what is wrong with my if-condition, but

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So I’ve been trying to figure out what is wrong with my if-condition, but I am getting nowhere. I am still new to R, so maybe I am not understanding some very basic concept here?

I have a dataframe (dc) to which I appended a column with logical “FALSE”. Now I want to change each FALSE into a TRUE based on the values in two columns of dc (dc$Probe and dc$Resp) that I specified using regexpr().

What it does so far is that, for both if-conditions, it changes each FALSE into TRUE regardless of the values in column 5 of dc. When I run the if-conditions seperately, I can see that they seem to be working fine on the OR-part of the condition, meaning the code only generates TRUE when the strings in dc$Probe match one of the strings specified in the OR-part. However, the AND-part seems to be ignored? Thus, when I run the complete code, I get a column with only TRUE, which is not what I want.

Edit: I should get a TRUE only if the string in Probe ends in a certain pattern (as specified in either of the two if conditions I wrote) and if the corresponding value in Resp is a “100” for the patterns specified in my first condition or a “200” for the patterns specified in my second condition. Thus, for strings ending in (sg|s|w1|w3|s1|s2), Resp must be “100” to get a TRUE and for strings ending in (\d\dg|\d\d), Resp must be “200” to get a TRUE. All other cases should be FALSE. For example, if a string ends in s1 and the corresponding value in Resp is 200, the code should return FALSE.

Edit: Some example data:

>dc<-data.frame(Subject=rep("SN",6), item.c=(1:6),  Stim=c("XYZc02s03","XYZc01s30","XYZc02s29", "XYZc01s38", "XYZc02s11", "XYZc06w21"), Probe=c("XYzf02s03","XYZf01s30g","XYZf02s29w1","XYZf01s38sg","XYZf02s11s","XYZv06w21s1"), Resp=c(200, 100, 100, 100, 100, 200))

This is my code:

>dc$Resp<-as.character(dc$Resp) #column 5 in dc
 dc$Probe<-as.character(dc$Probe)

 dc$correct_response <- FALSE

 for (i in 1:nrow(dc)) {
     if (regexpr("^.*sg$", dc$Probe[i])==1 || regexpr("^.*s$", dc$Probe[i])==1 || regexpr("^.*w1$", dc$Probe[i])==1 || regexpr("^.*w3$", dc$Probe[i])==1 || regexpr("^.*s1$", dc$Probe[i])==1 || regexpr("^.*s2$", dc$Probe[i])==1 && dc[i,5]=="100") {(dc$correct_response[i]<- TRUE)}
     if (regexpr("^.*\\d\\dg$", dc$Probe[i])==1 || regexpr("^.*\\d\\d$", dc$Probe[i])==1 && dc[i,5]=="200") {(dc$correct_response[i]<- TRUE)}
}

Is there something wrong with the regular expressions I am using? I checked them with glob2rx() and it seems like they are ok…Is my use of “OR” (||) or/and “AND” (&&) incorrect? How do I implement the AND-part properly? I have also tried the following code for the AND-part, but it didn’t change anything:

regexpr("200", dc$Resp[i])==1

I read the R-help on regular expressions and control flow, but I still don’t see what I am doing wrong. Consulting other webpages on logical expressions did not help me either.

Please help!

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1 Answer

  1. Editorial Team

    Im wondering if it can all be reduced to the following:

    dc<- read.table(header=T,text="Subject item.c      Stim       Probe Resp
      SN      1 XYZc02s03   XYzf02s03  200
      SN      2 XYZc01s30  XYZf01s30g  100
      SN      3 XYZc02s29 XYZf02s29w1  100
      SN      4 XYZc01s38 XYZf01s38sg  100
      SN      5 XYZc02s11  XYZf02s11s  100
      SN      6 XYZc06w21 XYZv06w21s1  200")

cond1<-regexpr("^.*(sg|s|w1|w3|s1|s2)$", dc$Probe)==1 & dc$Resp==100
cond2<-regexpr("^.*(\\d\\dg|\\d\\d)$", dc$Probe)==1 & dc$Resp==200
dc$correct_response<-cond1|cond2
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