Category: Software Development

Visualizing 350 million people movement in US

A screenshot from 48 states animation (during the time of hurricane Katrina)

I worked on visualizing US address change records for last two months and my work has been published in company’s blog.
I originally started with getting high level pictures from Gephi but realized that Gephi wasn’t quite suited for visualizing what I wanted to convey. So I wrote a program in Java using processing library to gain finer control over some visual primitives for coloring, sizing and animation.

So head over and take a look at the post by clicking the link below.

How I built HN Browser(my first iOS app)

I am going to share my experience building an iOS app for the first time.


First some high-level summary.

  • iTunes App Store Link
  • Project start date : Mid October
  • Code start date : October 26th
  • First submission to App Store : November 14th
  • First approval : November 30th
  • Total hours : ~80 hours
  • Commits : 35
  • Tools used : github, xcode, asana, photoshop, testflight

Research phase (~30 hours)

I had some understanding about what was involved in application building in web but have never written an native mobile application before. Not only I had to familiarize myself with Objective-C syntax but had to learn about iOS SDK.

For the developers who are new to iOS development, I would recommend to follow some tutorials on the web.


Once I was familiar with Objective-C syntax, I also started reading/watching tutorials for iOS SDK. There are many tutorials on the web including YouTube videos but I found iOS SDK essential training on very helpful. So I watched all sessions and followed code examples. It was very important to follow code examples because often times there are hidden steps in explanations to avoid redundancy.


While I was learning about iOS and Objective-C, I spent some time to look at many screenshots of iPhone apps. It was important to identify different components of iOS applications so I could decompose them in my head to identify which UI elements were used. Good resource for this is iTunes app store and

  • – it is better to use iTunes for browsing

Coding Phase (~30 hours)

I came up with a name of the app(HackerNews Reader) to begin followed by a git repo on github and a project in Asana in order to keep track of tasks involved in building an app. One key lesson I learned was YOU SHOULD RESERVE YOUR APP NAME IN ITUNES CONNECT FIRST! I had to go through a lot of changes later because the app name wasn’t available in iTunes connect.

Screen Shot 2012-11-30 at 10.40.10 PMScreen Shot 2012-11-30 at 10.39.48 PM

I had a rule that I set with myself. At least one commit everyday. This rule was crucial for me to finish this app. I had a few iterations on the design but because the app itself was simple, I didn’t have to go through any dramatic change. The most time consuming part of coding was UI and I suspect it is because I wasn’t familiar with UI components in iOS SDK.

When I had problems, like everyone else, I searched Google and Stack Overflow. I will list some examples below.


As you can see, some of them are elementary but I had no idea how to implement because lack of knowledge on iOS SDK.

Launch/Test Phase (~20 hours)

I primarily used iPhone simulator and TestFlight to test on my iPhone.


My app was rejected once but it was hard to understand why. It said something like

We found the following issues with the user interface of your app:

Specifically, the app did not include iOS features. For example, it would be appropriate to use native iOS buttons and iOS features other than just web views, Push Notifications, or sharing.

So I added activityViewController so users can share article through Facebook, Email, and Twitter


And finally it was approved!

It was a lot of fun and I will continue to build something while I am learning more. I hope this post helps anyone who is thinking about building a mobile application.

Using Gephi to understand Gephi

I have been playing with an opensource software called Gephi for several months. I believe it is one of the best non-proprietary network visualization softwares currently out there. Gephi allows users to visualize, navigate and understand relational dataset such as social network data, quickly and efficiently. 0.8 beta which was just released less than a week ago includes some major enhancements and bug fixes.

Gephi is fairly big project with large sourcecode base. If you want to write plugins or modify sourcecode, it could be overwhelming in the beginning. Once you understand the structure, it gets easier but still non-trivial.

I was once trying to wrap my head around the structure of Gephi sourcecode and I thought it would be interesting to use Gephi to understand Gephi sourcecode.

I wrote a small script in Ruby to go through the sourcecode and lookfor import statement and created list of directional links from one class to the other. I made the script output a network file which I can open in Gephi to visualize. Since I was only interested in Gephi project, I decided to narrow down the scope to org.gephi only.

I ran one of the built-in layout algorithm, ForceAtlas 2, and colored the network by top-level module(below). Besides a pretty picture, you can see some clusters in the network but center of the network looks like there are many cross referencing.

In order to see more structure in the network, I grouped nodes based on their membership to modules(below). This shows inter-module dependencies of the sourcecode which is very interesting. Nodes are sized by the number of sub-classes and the thickness of edges represent the number of classes connecting different groups in this case, modules. You can see datalab being the largest module based on the number of sub-classes. The average degree is 10.6 which means, if you change sourcecode of a module, you have an average of 10.6 modules you should consider to make sure you don’t have any compatibility issue.

Last picture(below) shows a slightly granular view. Nodes are broken down by one sub-level. In this view, average degree is 7.7.

This was a helpful exercise for me. If I get a chance, I can do this for all previous versions of Gephi to visualize the project’s evolvement.

iOS 4 Multi-tasking UI Suggestion

So I ended up getting an iPhone 4 on Oct 1.
I like it. Screen is gorgeous, it is faster, etc.
But one thing I don’t like about the iOS 4 is the way it handles multi-tasking:

1. Launch an application.
2. Launch another application.
3. Double tap the home button to see the application you are running.
4. Hold one of the application icons to quit the application.

Although it is great to move between application without reloading, it is a burden to close the application.

So after thinking about it, I suggest this workflow:
1. Launch an application
2. Launch another application, which will automatically quit the previously opened application.
3. If you want the application to keep running in the background, you double tap the home button.
3-1. You should see your current application with a lower opacity and a “+” icon.
3-2. You tap on the “+” icon to keep it running even if you go to the home screen or to another application.
4. Quitting the application should be the same way as in the current iOS 4,  except your currently running application won’t have a ” –” icon. (current iOS 4 doesn’t show the icon of current application.)

Here’s a quick mockup to give you visual sense of the flow…
What do you think?

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jQuery Mobile Announced!

There are number of javascript frameworks out there to bring touch events to smart phones and tablets.
I am particularly interested of jQuery announcing their own because 1. The project I am working on uses jQuery and 2. jQuery has been my favorite JS framework.
I’ve tried Sencha, jQtouch, and others but I wasn’t happy with any of them. I will give jQuery Mobile a try and share the result with you shortly.

What is mongoDB?

The latest project that I am working on uses mongoDB as the database. mongoDB is a document-oriented database which is quiet different compare to relational database such as SQL. It stores full document(BSON format which is very similar to JSON) and you will be able to query by sending key-value bases BSON object. For example,


returns every document in products collection. but you will be able to send query like.

db.products.find({'kind' : 'apparel'})

This query looks for ‘kind’ attribute and return document where ‘kind’ attribute is ‘apparel’.