[R] to create a new variable based on values in other variables

Yuan Chun Ding ycd|ng @end|ng |rom coh@org
Tue Apr 7 21:05:32 CEST 2020

Hi Thierry,

the values in the example data frame are fake numbers, my original data frame has hundreds of row and values are in wide range, not min or max of two variables, also the number 23 is also different in different data frames.

I agree I need to use vectorized ifelse, but I got confused when there are more than two conditions inside of ifelse function. I will look into ifelse function

Thank you,


From: Thierry Onkelinx [thierry.onkelinx using inbo.be]

Sent: Tuesday, April 7, 2020 11:48 AM

To: Yuan Chun Ding

Cc: r-help mailing list

Subject: Re: [R] to create a new variable based on values in other variables

Dear Ding,

It seems that you are looking for the ifelse() function. Clear use of pmax() and pmin() reduces the number of if statements.

m1 <- c(12, 23, 22, 23)
m2 <- c(23, 23, 3, 5)

Ravg <- ifelse(

  pmax(m1, m2) == 23,

  pmin(m1, m2),

  (m1 + m2) / 2


Best regards,

ir. Thierry Onkelinx
Statisticus / Statistician

Vlaamse Overheid / Government of Flanders


Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance 

thierry.onkelinx using inbo.be

Havenlaan 88 bus 73, 1000 Brussel



To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher

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Op di 7 apr. 2020 om 20:35 schreef Yuan Chun Ding <ycding using coh.org>:

Hi R users,

I want to create a new variable, Ravg, in data frame tem2 based on values of two other variables m1 and m2.

the condition:

if m1 = 23 and m2 =23 then Ravg =23; 

else if m1 != 23 and m2=23 then Ravg =m1;

else if m1 =23 and m2 !=23 then Ravg=m2;

else Ravg=average of m1 and m2;

the Ravg variable should be  same as  m3 variable in the following small example.

my R code did not generate errors but not generate a new variable.

Ravg <- "rare_allele"

  tem2 <-data.frame(m1=c(12, 23, 22, 23), m2=c(23, 23, 3, 5), m3 =c(12, 23, 12.5, 5))

  for (r in 1:nrow(tem2)) { 

  if (tem2$m1[r] ==23 & tem2$m2[r] ==23) {

    tem2[[Ravg]][r] ==23} else if(tem2$m1[r] ==23 & tem2$m2[r] !=23){

    tem2[[Ravg]][r] ==tem2$m2[r]} else if (tem2$m1[r] !=23 & tem2$m2[r] ==23) {

    tem2[[Ravg]][r] ==tem2$m1[r]} else {

    tem2[[Ravg]][r] == mean(tem2$m1[r] + tem2$m2[r])}


Thank you,





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