Group list of strings by common substring

Question

I have a list of strings for example:

("2019_FOO_BAR.1_12"
 "2019_FOO_BAR.1_13"
 "2018_FOO_BAR.1_12"
 "2019_FOO_XYZ.1_14"
 "2017_FOO_BAR.1_14"
 "2017_FOO_XYZ.1_12"
 "2019_FOO_XYZ.1_13")

I want to group them by common substring after first underscore and before the dot.

In this example I have 2 unique substrings FOO_BAR and FOO_XYZ. But longer list may have N unique substrings.

I want the result to look like this:

(["2019_FOO_BAR.1_12" "2019_FOO_BAR.1_13" "2018_FOO_BAR.1_12" "2017_FOO_BAR.1_14"]
 ["2017_FOO_XYZ.1_12" "2019_FOO_XYZ.1_13" "2019_FOO_XYZ.1_14"])

So each substring is grouped in a separate list

What have you tried so far?

akond
– akond

2019-08-20 18:18:29 +00:00
Commented Aug 20, 2019 at 18:18 — akond
– akond, Commented Aug 20, 2019 at 18:18

meerkat · Accepted Answer · 2019-08-20 18:37:44Z

4

I think you are looking for a group-by

(def test-data '("2019_FOO_BAR.1_12"
                 "2019_FOO_BAR.1_13"
                 "2018_FOO_BAR.1_12"
                 "2019_FOO_XYZ.1_14"
                 "2017_FOO_BAR.1_14"
                 "2017_FOO_XYZ.1_12"
                 "2019_FOO_XYZ.1_13"))


(defn string-to-key [^String input-string]
  (let [first-spliter (.indexOf input-string "_" )
        second-spliter (.indexOf input-string "." )]
    (.subSequence input-string (+ 1 first-spliter) second-spliter)))

So you can get exactly what you are looking for with:

(vals (group-by string-to-key test-data))

edited Aug 20, 2019 at 18:37

meerkat

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answered Aug 20, 2019 at 18:30

r00tt

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1 Comment

meerkat Over a year ago

Thanks. I was thinking using group-by but wasn't sure about splitting function implementation.

leetwinski · Accepted Answer · 2019-08-20 19:33:50Z

4

good candidate for regex:

user> (vals (group-by (partial re-find #"_.*?\.") data))

;; => (["2019_FOO_BAR.1_12"
;;      "2019_FOO_BAR.1_13"
;;      "2018_FOO_BAR.1_12"
;;      "2017_FOO_BAR.1_14"]
;;     ["2019_FOO_XYZ.1_14" "2017_FOO_XYZ.1_12" "2019_FOO_XYZ.1_13"])

answered Aug 20, 2019 at 19:33

leetwinski

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2 Comments

meerkat Over a year ago

Thanks. Nice and concise!

r00tt Over a year ago

Regular Expressions: Now You Have Two Problems :)

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