gistfile1.txt

strs = c("nomatch", "Odum 1969", "2001FACE_3b", "1800", "sdfghj1928qwer")
strs_yrs = gsub(".*((19|20)[0-9]{2}).*", "\\1", strs)
strs_yrs
# [1] "nomatch" "1969"    "2001"    "1800"    "1928"   
# Oops, strings with no year (or year from wrong century) are returned unchanged! Let's remove them separately:
strs_haveyr = grepl("(19|20)[0-9]{2}", strs)
strs_yrs[!strs_haveyr] = ""
strs_yrs
# [1] ""     "1969" "2001" ""     "1928"

# (N.B. assumes only one year per string -- if several, will return only 1st one.) 

Thanks for this! I'm just trying it now.
*** This works great *** Just saved me going through a long list of differently formatted references to extract the year of publication.