Question

I’m using Clojure to parse and analyze XML files.
Here is a sample:

BSS:17,NSVC:1
BSS:17,NSVC:4
BSS:17,NSVC:5
BSS:17,BTSM:0,BTS:3
BSS:17,BTSM:0,BTS:4
BSS:17,BTSM:0,BTS:5
BSS:17,BTSM:1,BTS:0
BSS:17,BTSM:1,BTS:1
BSS:17,BTSM:1,BTS:2
BSS:17,BTSM:1,BTS:3

I’m interested in that last value (a value after the last comma but before the last : , NSVS and BTS in my case), digits after them don’t matter.
How to extract that last value in the previous strings?

Answer 1

You can use this function to process the individual lines:

(defn lastval [s]
  (second (re-find #",([^,:]+):\d*$" s)))
                 ;   ^ the comma preceding the interesting section
                 ;    ^ the part in parens will be captured as a group
                 ;     ^ character class meaning "anything except , or :"
                 ;            ^ the colon after the interesting section
                 ;             ^ any number of digits after the colon
                 ;                ^ end of string
          ; ^ returns a vector of [part-that-matches, first-group];
          ;   we're interested in the latter, hence second

NB. this returns nil if the regex doesn’t match.

E.g.:

user> (lastval "BSS:17,BTSM:0,BTS:3")
"BTS"

If you later want to extract all the information in easy-to-work-with bits, you can use

(defn parse [s]
  (map (juxt second #(nth % 2)) (re-seq #"(?:^|,)([^,:]+):(\d+)" s)))

E.g.

user> (parse "BSS:17,BTS:0,BTS:3")
(["BSS" "17"] ["BTS" "0"] ["BTS" "3"])