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sortingclojurehashmap

How do I use sort-by on nested maps when the keys are strings, not keywords?

Related question.

This works with keywords

(sort-by (comp :rank second) > 
  {:1 {:bar "something" :rank 10} :2 {:bar "other" :rank 20}})

This fails when it's a string

(sort-by (comp "rank" second) >
  {:1 {:bar "something" "rank" 10} :2 {:bar "other" "rank" 20}})

Error message is "Execution error (ClassCastException) at java.util.TimSort/countRunAndMakeAscending (TimSort.java:355). java.lang.String incompatible with clojure.lang.IFn"

I take it the problem is that keywords can be a function but strings cannot be functions. What is the solution? I've tried playing around with get without success.

Solution

  • comp composes functions, so you'll need a function that can get the key by string:

    user> (->> {:1 {:bar "something" "rank" 10} :2 {:bar "other" "rank" 20}}
           (sort-by (comp #(get % "rank") second) >))
([:2 {:bar "other", "rank" 20}] [:1 {:bar "something", "rank" 10}])