How do I count the number of words in a text (string)?

Use the stringi package and stri_count:

require(stringi)
str <- c(
"this is a string current trey",
"nospaces",
"multiple    spaces",
"   leadingspaces",
"trailingspaces    ",
"    leading and trailing    ",
"just one space each")

> stri_count(str,regex="\\S+")
[1] 6 1 2 1 1 3 4

You can try

sapply(gregexpr("\\S+", x), length)
## [1] 6 2 1 1

Or as suggested in comments you can try

sapply(strsplit(x, "\\s+"), length)
## [1] 6 2 1 1