how to sort by key a Dictionary object?

On 25.08.2009, at 23:31, Randal L. Schwartz wrote:

There might be a far better way.. but I found this in a few minutes.

Someone should make a Squeak version of

       http://xkcd.com/627/

- Bert -


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I know this was already covered but to simplify the explination for the beginner:

 

Sort is automatic for Dictionaries.

 

| dict |
dict := Dictionary new.
dict at: '3c' put: 'object 3c'.
dict at: '1a' put: 'object 1a'.
dict at: '2b' put: 'object 2b'.
dict

 

Evaluating the code with "Print It" will respond:

a Dictionary('1a'->'object 1a' '2b'->'object 2a' '3c'->'object 3a' )

 

----------------------

 

A useful capability of Dictionaries is merging files by key.

Add old objects then overwriting with new objects and sorting is automatic.

 

| dict |
dict := Dictionary new.
dict at: '3c' put: 'object 3c'.
dict at: '1a' put: 'object 1a'.
dict at: '3c' put: 'new object 3c'.
dict

 

 a Dictionary('1a'->'object 1a' '3c'->'new object 3c' )

 

On 25.08.2009, at 23:52, r00t uk wrote:

Bert - I don't think creating a Squeak version of that would have helped anybody new to squeak/smalltalk.

Right, in this case not, but that's not what I meant primarily. Should have changed the subject and moved to squeak-dev, sorry. I'll make up for it, see below [*].

I meant that I've never seen a graphical explanation of what Randal did in these "few minutes" to find out. It's what experienced Smalltalkers do all the time, and Squeak provides powerful ways of finding out about itself, but they are not obvious to newbies.

Usually we don't even mention that it took us a minute to find out, so beginners get the impression that it's "all in our heads". It's not (not *all* anyway) but the tools allow us to find out quickly. Faster than looking up documentation indeed, which we can't really proof because of the lack of it ;)

  Cookbook wiki maybe?

2009/8/25 Bert Freudenberg <[hidden email]>

On 25.08.2009, at 23:31, Randal L. Schwartz wrote:

There might be a far better way.. but I found this in a few minutes.

Someone should make a Squeak version of

       http://xkcd.com/627/

- Bert -

[*] Here's what I'd do:

Make a little test case in a workspace:

| dict |

dict := {'a' -> 'first'. 'b' -> 'second'. 'c' ->'third'} as: Dictionary.

dict 

This intentionally does not use integers as keys, because that's what's special about Dictionaries. (and in fact I didn't really open a workspace but typed it right in the browser I happened to have open. Saves a second)

When I printed the expression above, the elements *were* sorted by key. So this may be chance, but I wanted to see. So I double-clicked Dictionary, pressed cmd-b to bring up a browser, clicked in the right pane with all the methods, and pressed p, to find printing-related methods (I should have clicked the "printing" protocol but usually methods are named more sanely than they are categorized). Anyway this took me right to the "printElementsOn: aStream" which indeed sorts. That could be a template for your own solution.

But in any case the print string of the dictionary is not helpful to show the problem. So:

| dict |

dict := {'a' -> 'first'. 'b' -> 'second'. 'c' ->'third'} as: Dictionary.

dict asArray

Yes, this printed #('second' 'third' 'first'), so now we need to sort. I have the idiom in my head but I typed in in anyway to verify

| dict  |

dict := {'a' -> 'first'. 'b' -> 'second'. 'c' ->'third'} as: Dictionary.

dict keys asSortedCollection collect: [:key | dict at: key]

And this indeed gives  an OrderedCollection('first' 'second' 'third')

So if I had sent an answer to your question I probably would have just pasted the line

dict keys asSortedCollection collect: [:key | dict at: key]

not even mentioning that it took me a minute to verify, and that en passant I discovered that dictionary printing is sorted for a couple of years already, which I had not noticed ;)

Comparing this to Randal's suggestion I'd say that mine feels more "Smalltalky". Accessing the associations in a dictionary directly feels unclean. Maybe because it breaks the abstraction, associations are an implementation detail of dictionaries. It's unlikely this will ever change and accessing the associations is fine, but still ;)

- Bert -

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