Using ifelse in R

Question

I am trying to code the following statement in R with if and ifelse.The sample data is trial and x,y,and z are columns of trial).

S

Answer 1

I would use transform twice for example:

trial <- data.frame(x=c(-1,1,2),y=c(1,-2,3),z=c(1,-5,5))
trial <- transform(trial,l = ifelse(x>0,ifelse(y > 0,2,5),NA))
transform(trial,m = ifelse(x>0,ifelse(z>0,l+2,5),NA))

   x  y  z  l  m
1 -1  1  1 NA NA
2  1 -2 -5  5  5
3  2  3  5  2  4

Note that I assign NA for case x < 0. You can use a one transform like this for example:

trial <- data.frame(x=c(-1,1,2),y=c(1,-2,3),z=c(1,-5,5))
transform(trial,l <- ifelse(x>0,ifelse(y > 0,2,5),NA),
                         m = ifelse(x>0,ifelse(z>0,l+2,5),NA))
  x  y  z c.NA..5..2.  m
1 -1  1  1          NA NA
2  1 -2 -5           5  5
3  2  3  5           2  4

But personally I would prefer the first one for readability besides the fact you need maybe change column names.

Answer 2

If you want to use ifelse and nest things you could do something like this

test <- data.frame(x = 2, y = 5, z = 3)
with(test, ifelse(z > 0 & x > 0 | y > 3, "yes", "no"))

In this case you're using logical operators to guard the output. You'll still get "no" if z <= 0, but you can deal with that pretty easily.

with(test, ifelse(z > 0, ifelse(x > 0 | y > 3, "yes", "no"), NA))

Nested ifelse statements can get hard to follow in any language, so consider matching or switch statements if you end up with more than 3 of them.