Monday, January 17, 2011

Reddit "Top"

Reddit has an API that can be used for accessing much of the information available through their website. We can retrieve a JSON list of recent stories posted to any subreddit by going to$NAME. You can experiment with this in the Factor listener - to retrieve top stories for the programming subreddit:

( scratchpad ) USING: http.client json.reader ;

( scratchpad ) ""
               http-get nip json> .

Someone once used the API to build a reddit-top program for monitoring top stories from the console. We will use Factor vocabularies to scrape Reddit and produce something similar:

We start by building a (subreddit) helper word to retrieve the JSON response for a particular subreddit, extracting the top stories, and returning an array of hashtables (one for each of the top stories).

: (subreddit) ( name -- seq )
    "" sprintf http-get nip
    json> { "data" "children" } [ swap at ] each
    [ "data" swap at ] map ;

We can then define a story tuple, with a slot for each attribute returned by the API.

TUPLE: story author clicked created created_utc domain downs
hidden id is_self levenshtein likes media media_embed name
num_comments over_18 permalink saved score selftext
selftext_html subreddit subreddit_id thumbnail title ups url ;

Once we have that, we can use the set-slots word from my previous post on setting attributes to build a subreddit word that retrieves the top stories as objects:

: subreddit ( name -- stories )
    (subreddit) [ story new [ set-slots ] keep ] map ;

Thats all we need to build the subreddit-top word demonstrated in the beginning:

  1. Retrieve the top stories for a given subreddit.
  2. Loop over each story.
  3. Format and print the relevant attributes.
: subreddit-top ( subreddit -- )
    subreddit [
        1 + "%2d. " printf {
            [ title>> ]
            [ url>> ]
            [ score>> ]
            [ num_comments>> ]
                created_utc>> unix-time>timestamp now swap time-
                duration>hours "%d hours ago" sprintf
            [ author>> ]
        } cleave
        "%s\n    %s\n    %d points, %d comments, posted %s by %s\n\n"
    ] each-index ;

This (and some code for users and comments) is available on my Github.

1 comment:

Redline6561 said...

Awesome article that really shows off Factor's libs. Keep 'em coming!