1
給定下面的函數,它帶有兩個參數(csv-data1和csv-data2,只有兩行的矢量矢量和保證的不匹配,所以在我的輸出中會得到cmp-val)。爲什麼有條件減少原因無返回?
(defn test-key-inclusion
"Accepts csv-data param and an index, a second csv-data param and an index,
and searches the second csv-data instances' rows (at index) to see if
the first file's data is located in the second csv-data instance."
[csv-data1 pkey-idx1 csv-data2 pkey-idx2 lnam-idx fnam-idx]
(reduce
(fn [out-log csv-row1]
(let [cmp-val (nth csv-row1 pkey-idx1 nil)
lnam (nth csv-row1 lnam-idx nil)
fnam (nth csv-row1 fnam-idx)
temp-rc (first (key-pres? cmp-val pkey-idx2 csv-data2))]
(if-not (nil? cmp-val)
(concat out-log (sorted-map cmp-val (vector lnam fnam))))))
{}
csv-data1))
有了這個條件的功能,
(if-not (nil? cmp-val)
(concat out-log (sorted-map cmp-val (vector lnam fnam))))))
減少返回nil。
這是爲什麼?
如果你不提供備用(否則)條款,是不是該分支「重返」'默認nil'? – 2012-04-12 20:03:47