R using diff: non-numeric argument to binary operator error

Question

We parse a CSV-File with some numbers with the following command:

tt <- read.table("test2.csv",sep=";",stringsAsFactors=FALSE)

And it works. Printingtt[1,] yields a nice vector and sd(tt[1,]) is sensible.

However, when we try

diff(tt[1,])

The command-line returns the error:

Error in r[i1] - r[-length(r):-(length(r) - lag + 1L)] :
    non-numeric argument to binary operator error

Why is that? Any ideas?

Answer 1

I presume that in your tt[1,], that

class(tt[1,])
# [1] "data.frame"

So if you use as.numeric, you should be okay. Try this:

diff(as.numeric(tt[1,]))

---

Here's an example that we can inspect:

tt <- data.frame(x = 1, y = 2)
is.vector(tt[1,])
# [1] FALSE
class(tt[1,])
# [1] "data.frame"
diff(tt[1,])
# Error in r[i1] - r[-length(r):-(length(r) - lag + 1L)] : 
#   non-numeric argument to binary operator
as.numeric(tt[1,])
# [1] 1 2
diff(as.numeric(tt[1,]))
# [1] 1