How do I correctly use the threading macros?

Question

My question is how can I get one of Clojure's threading macros to work in my specific case? Thank You. I am getting this error: ``` (IllegalArgumentException Don't know how to create ISeq from: bene_csv.core$test_key_exclusion$fn__346 clojure.lang.RT.seqFrom (RT.java:487) ``` When I call this function: ``` bene-csv.core=> (test-key-exclusion bene-data 1 gic-data 0 2 3) ``` Given this code -- working solution without threading macro is commented out -- ``` (defn ret-non-match-rows "Expects a sequence of sequences, like what is returned from clojure-csv. Returns nil if there's a match; else returns failing row." [s-o-s cmp-col-idx inq-row-idx inq-row] (let [inq-row inq-row] (loop [[row & remain-seq] s-o-s pos 0] (let [cmp-val (nth inq-row inq-row-idx nil)] (cond (not row) inq-row (= cmp-val (nth row cmp-col-idx)) nil :not-found (recur remain-seq (inc pos))))))) (defn test-key-exclusion "This function takes csv-data1 (the includees) and tests to see if each includee is in csv-data2 (the…

Accepted Answer

You are using the "thread-first" macro, but you should be using the "thread-last" macro instead. The "thread-last" macro, which is bound to the symbol `->>`, does the same thing as the "thread-first" macro except it inserts the forms as the last argument instead of the first.

So your code would look something like this:

```
(->> (map #(ret-non-match-rows csv-data2 pkey-idx2 pkey-idx1 %1) csv-data1)
     (filter (complement nil?))
     (map (fn [row]
       (vector (nth row pkey-idx1 nil)
               (nth row lnam-idx nil)
               (nth row fnam-idx nil))))))
```

How do I correctly use the threading macros?

Solution

Problem