在R中提取相应的值

Question

I am trying to find rows in su19$q2 marked "Yes", and from there find its corresponding value (names of schools) in su19$q1 . However, everything I am trying seems to not work.

su19$q1[su19$q2 == "Yes"]

I do not understand why this is not working.

My expectation is that for every "Yes" response in q2, a list is returned of its corresponding school from column q1.

Answer 1

This should work:

su19$q1[which(su19$q2 == "Yes")]

The which() function returns the indices where the given vector is "True". In your example the expression su19$q2 == "Yes" returns a vector of either True of False depending if the equality holds or not (see https://www.rdocumentation.org/packages/base/versions/3.6.1/topics/which )

Answer 2

I am creating a new answer as adding code is not possible in comments

su19 <- data.frame(q1 = c("Santiago Canyon College","College of 
       Alameda","Cerritos College","Cuyamaca college","Cypress College","Folsom Lake 
       College"), q2= c("Yes","Yes","Yes","Yes","Yes","Yes"),stringAsFactors= FALSE)

                        q1  q2
 1 Santiago Canyon College Yes
 2      College of Alameda Yes
 3        Cerritos College Yes
 4        Cuyamaca college Yes
 5         Cypress College Yes
 6     Folsom Lake College Yes

@Chelmy88 solution

su19$q1[which(su19$q2 == "Yes")]
[1] "Santiago Canyon College" "College of Alameda"      "Cerritos College"        "Cuyamaca college"        "Cypress College"        
[6] "Folsom Lake College" 

my solution

su19[which(su19$q2 == "Yes"),]$q1
[1] "Santiago Canyon College" "College of Alameda"      "Cerritos College"        "Cuyamaca college"        "Cypress College"        
[6] "Folsom Lake College" 

If you don't have a data.frame , but vectors only

q1 <- c("Santiago Canyon College","College of Alameda","Cerritos College","Cuyamaca college","Cypress College","Folsom Lake College")
q2 <- c("Yes","Yes","Yes","Yes","Yes","Yes")

su19$q1[which(su19$q2 == "Yes")]
[1] "Santiago Canyon College" "College of Alameda"      "Cerritos College"        "Cuyamaca college"        "Cypress College"        
[6] "Folsom Lake College"