Fold That Story–iOS

Late last year I released Fold That Story to the Edmodo app store as a web application. Then earlier this year I made it more broadly available as a web application that was open to anyone. I’ve now released the iOS version that allows teachers and students to play using mobile devices.

Fold That Story is a creative writing game where students and teachers write a story one section at a time. The catch is that students can only read the last section. This means that a story can evolve and take a number of plot twists as the story progresses. The app focuses on teacher controls such as:

• The ability for a teacher to change the display name of a student.
• Teachers can view and edit a section at any time.
• A profanity filter removes any nasty words.
• Students can be made read only and controlled by the teacher.

The app can be downloaded from the App Store.

Pay With Pin – Android

I wanted to experience porting over a Xamarin iOS app to Android and decided that my Pay With Pin app was a good candidate. The app is pretty straight forward, it has a number of tabs that display information, a couple of forms for user input and a fair bit of common code that works with the Pin API.

I was able to reuse almost 100% of the common code that works with the Pin API, it’s really impressive. Then binding data to the UI and building the UI was pretty straight forward. I still think that iOS development is easier, the process is more refined and requires less effort. I think the end result on iOS is better.

A few screenshots of the app:

Pay With Pin lets you create and charge customers, view charges and process new charges. You could easily use it at to run a market stall on the weekend or something like that.

It can be downloaded on Google Play here.

April Fool

Last week was Aprils fools day, which means that for the days before and after you tend to be especially skeptical about the things you read on the web. So when I read that Redis had added one of my favorite algorithms the HyperLogLog I was in two minds as to whether this was real or not. The detailed analysis that Salvatore put together was very convincing but the date of the post was really off-putting.

If you haven’t heard of HyperLogLog before, it’s a method to work out the cardinality of some measure. Which in non-set based terms means, being able to efficiently count the number of unique items. One of the best implementations I’ve seen is the HyperLogLog Postgresql extension. This lets you define a new native data type. To use it you must use the various hash methods when inserting data, this is a required part of the HyperLogLog algorithm. The examples used in the readme.md page of the Github repo shows the real power of the extension.

Consider a data warehouse that stores analytic data;

-- Create the destination table
CREATE TABLE daily_uniques (
    date            date UNIQUE,
    users           hll
);

-- Fill it with the aggregated unique statistics
INSERT INTO daily_uniques(date, users)
    SELECT date, hll_add_agg(hll_hash_integer(user_id))
    FROM facts
    GROUP BY 1;

Imagine that we have inserted a number of items into this table from some fact table. We can then query the table:

SELECT date, hll_cardinality(users) FROM daily_uniques;

Now the queries will look like:

SELECT hll_cardinality(hll_union_agg(users)) FROM daily_uniques WHERE date >= '2012-01-02'::date AND date <= '2012-01-08'::date;

or

SELECT date, #hll_union_agg(users) OVER seven_days
FROM daily_uniques
WINDOW seven_days AS (ORDER BY date ASC ROWS 6 PRECEDING);

Remember as well that the amount of storage space used here is absolutely minimal, Often in the order of bytes.

So as you can see HyperLogLog is really cool and it’s a great credit to the team behind Redis for bringing this into the product. Even if they do publish the announcement on April Fools day

Redis is a fantastic tool, it is so much more than just a memcache replacement, I like to think of it as Comp Sci in a box. It has all of the goodies: Lists with set based operations, sliding caches, queues, single threaded event based goodness. It’s a very exciting tool and I’m very glad to see it evolve.