Note to self: column selection and row filtering in dplyr

As I’m no longer quite the spring chicken I once was, and information seems to be harder to get to stick in the brain, here’s the first in a series of small notes to myself (and anyone else for whom they might be useful) of things that I repeatedly have to look up.

If I have a data frame in R:

X1	X2	Y1
A1	C1	E1
A2	C2	E2
B1	D1	F1
B2	D2	F2

and I want to select columns whose name begins with a string, the syntax is:

df %>% dplyr::select(dplyr::starts_with("X"))

X1	X2
A1	C1
A2	C2
B1	D1
B2	D2

But if I want to filter to include only rows whose value (in a particular column) starts with a certain string, then I can use the stringr package:

df %>% dplyr::filter(stringr::str_starts(X1, "A"))

X1	X2	Y1
A1	C1	E1
A2	C2	E2