subset data frame by complex pattern of column names

Question

I have a dataset that looks like the following:

• two rounds of data (.t0 and .t1)
• multiple scales (this and

Answer 1

This works for your example:

dat[c("id", grep("(this|that)\\d+[a-z]?\\.", names(dat), value = TRUE))]

where:

1. \\d+ is for one or more digits
2. [a-z]? is for zero or one lowercase letter
3. \\. is for the dot

If you want to build a pattern dynamically for various scales, you can do:

scales <- c("this", "that")
pattern <- sprintf("(%s)\\d+[a-z]?\\.", paste(scales, collapse = "|"))
dat[c("id", grep(pattern, names(dat), value = TRUE))]