[R] Sum of a couple of variables of which a few have NA values

[Petra Opic]

Dear everyone,

I have looked all over the internet but I cannot find a way to solve my problem.

In my data I want to sum a couple of variables. Some of these
variables have NA values, and when I add them together, the result is
NA

dat <- data.frame(
id = gl(5,1),
var1 = rnorm(5, 10),
var2 = rnorm(5, 7),
var3 = rnorm(5, 6),
var4 = rnorm(5, 3),
var5 = rnorm(5, 8)
)
dat[3,3] <- NA
dat[4,5] <- NA

> dat
 id      var1     var2     var3     var4     var5
1  1  9.371328 7.830814 5.032541 3.491053 7.626418
2  2 10.413516 7.333630 6.557178 1.465597 8.591770
3  3 10.967073       NA 6.674079 3.946451 7.251263
4  4  9.900380 7.727111 5.059698       NA 6.632962
5  5  9.191068 7.901271 6.652410 2.734856 8.484757

attach(dat)

dat$sum <- var2 + var3 + var4 # I think I'm doing this wrong, but I
don't know what command to use

> dat
  id      var1     var2     var3     var4     var5      sum
1  1  9.371328 7.830814 5.032541 3.491053 7.626418 16.35441
2  2 10.413516 7.333630 6.557178 1.465597 8.591770 15.35640
3  3 10.967073       NA 6.674079 3.946451 7.251263       NA
4  4  9.900380 7.727111 5.059698       NA 6.632962       NA
5  5  9.191068 7.901271 6.652410 2.734856 8.484757 17.28854

I would like to omit the values of NA and just sum the rest.

I tried to use rowSums() but that sums an entire row and I only need a
few variables.

Does anyone know how to do this?

Thanks in advance,
Petra