如何在Clojure中将哈希图列表转换为一个hasmap？

Question

I have a list which looks like this:

({:course 2, :mark 9} {:course 5, :mark 8} {:course 6, :mark 10})

And i want to convert it to hashmap:

{:2 9 :5 8 :6 10}

List was created from mysql database, i dont know can i get that datas from database in some other format, which will be easier to convert to one hashmap, i used java.jdbc query function.

Can anybody help me?

Answer 1

(fn [data] (into {} (map (juxt :course :mark) data)))

on

(list {:course 2, :mark 9} {:course 5, :mark 8} {:course 6, :mark 10})

produces

{2 9, 5 8, 6 10}

The keyword function does not accept numbers as arguments, so I don't think you can get quite what you were looking for. But digits are as good keys as keywords anyway.

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Wrong! As others have demonstrated, Clojure accepts digit strings as keywords. We can adapt the above to use such:

(fn [data] (into {} (map (juxt (comp keyword str :course) :mark) data)))

on

(list {:course 2, :mark 9} {:course 5, :mark 8} {:course 6, :mark 10})

produces

{:2 9, :5 8, :6 10}

But, as I've said, I think this is needlessly risky. Why not just use the numbers as keys?

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Further to using digit (strings) as keywords:

The reader doc about symbols says

• Symbols begin with a non-numeric character ...
• Keywords are like symbols, except: ... (further restricted)

Answer 2

Another variant. (Probably less efficient than Thumbnail's if you've got a lot of data.)

(zipmap (map (comp keyword str :course)  data)
        (map :mark data))

where data is in the format specified in the question.