Extract some filename annotations using regex

extract_annotations.R

library(stringr)

data_path <- 'somefolder/planet04_rgbn_c9_r8.txt'

# We want to extract 9 and 8
basename(data_path)

# Too many numbers
str_extract_all(basename(data_path), "([0-9]+)")
# [[1]]
# [1] "04" "9"  "8"

# Right numbers, but don't want _c and _r
str_extract_all(basename(data_path), "(_c|_r)([0-9]+)")
# [[1]]
# [1] "_c9" "_r8"

# Right number, missing 8
str_extract_all(basename(data_path), "(?<=c)\\d+")
# [[1]]
# [1] "9"

# Correct solution
str_extract_all(basename(data_path), "(?<=(_c|_r))\\d+")
# [[1]]
# [1] "9" "8"