Question

I have the following data frame:

structure(list(Species = 1:4, Ni = c(1, NA, 1, 1), Zn = c(1, 
1, 1, 1), Cu = c(NA, NA, 1, NA)), .Names = c("Species", "Ni", 
"Zn", "Cu"), row.names = c(NA, -4L), class = "data.frame")

and I would like to get a vector containing all the species where Ni = 1, Zn = 1 and Cu = NA. So in this example that would be (1,4)

I thought I could have a try with the R script select * from where, but I can’t seem to install the package RMySQL on RStudio (R version 2.15.1).

Answer 1

df <- structure(list(Species=1:4,Ni=c(1,NA,1,1),Zn=c(1,1,1,1),Cu=c(NA,NA,1,NA)),
      .Names=c("Species","Ni","Zn","Cu"),row.names=c(NA,-4L),class="data.frame")

with(df, Species[Ni %in% 1 & Zn %in% 1 & Cu %in% NA])
[1] 1 4

Rather than using Ni == 1 you should use Ni %in% 1, as the former will return NA elements where Ni is NA. Cu %in% NA produces the same result as is.na(Cu).

with(df, Species[Ni == 1 & Zn %in% 1 & Cu %in% NA])
[1] 1 NA 4

Note though that Ni == 1 used in subset, as in @MadScone’s answer, does not suffer from this (which came as a surprise to me).

subset(df, Ni == 1 & Zn == 1 & is.na(Cu), Species)
  Species
1       1
4       4