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as = <|1 -> 2.2, 2 -> 3.4, 3 -> 8.1|>;

I don't understand the following:

as[[1]]

2.2

But I expected to see

<|1 -> 2.2|>

On the other hand:

as[[1 ;; 1]]

<|1 -> 2.2|>

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    $\begingroup$ It;s like as[[{1}]] and if you have other head than association, it will be kept too. $\endgroup$
    – Kuba ♦
    Nov 3, 2015 at 20:07
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    $\begingroup$ When you do list[[1]] you don't expect to get a list so why do you expect association[[1]] to give an association? $\endgroup$
    – Simon Woods
    Nov 3, 2015 at 20:31
  • $\begingroup$ Right, but one could expect 1->2.2 $\endgroup$
    – eldo
    Nov 3, 2015 at 20:38
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    $\begingroup$ An association is not a list of rules. It's a different animal. Your intuition is correct if you do it on Normal[as]. $\endgroup$
    – Philip Maymin
    Nov 3, 2015 at 21:56

2 Answers 2

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Probably should be handled by KeyTake:

KeyTake[as, 1]

<|1->2.2|>

Also works with multiple "selections":

KeyTake[as, {1, 3}]

<|1 -> 2.2, 3 -> 8.1|>

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The difference could be related to the fact that Part (as[[1]]) treats associations transparently while as[[1;;1]] (i.e. as[[1~Span~1]]) is equivalent to Take[as[1,1]], and Take does not treat associations transparently.

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