one me; one keyboard

So, I took my GRE …

October 13, 2009 – 10:38 pm

… and scored pretty well. 1520, to be exact.

For most of the people I know, the biggest hurdle to getting a good score in the GRE was our vocabulary. Most of us have our own way of learning the various word lists available in the market. Mine involved a book, a software made in Visual Basic that kept track of difficult words, and a few spreadsheets.

Looking back, I feel there’s one basic rule to revising -

revise that which you did not know the last time you revised

With this approach, each subsequent revision contains fewer words than the last one, you don’t waste time revising the easy words, and hopefully end up with very few difficult words. Of course, you need to keep doing a holistic revision every now and then, so that you don’t forget what you already knew.

Keeping this in mind, Pascal and I made “Shabd”¹. For now, Shabd is hosted at http://wl.sandesh247.com/, and the source is hosted at http://code.google.com/p/shabd. All contributors are welcome.

For now, my deployment has around 5000 words, aggregated from various word lists. You can use the software without logging in. However, the true benefits can only be had if you’re logged in – the software keeps track of all the words you know, or don’t, and can present customized word lists later on. It allows you to go through your most difficult words, or the words you didn’t know the last time you saw them (in accordance with my basic rule to revising stuff).

Give it a try. Your password are salted and hashed, they aren’t going anywhere. There’s no way to change them as yet, so cling on to them while we add support. Also, we need a way to have custom word lists (tags?), and host more flash cards (say, of the French language). The user interface too, leaves a lot to be desired. And then there are things that you’ll find wrong with it. Please log all such ideas and problems at http://code.google.com/p/shabd/issues/list. You’ll need a Google account for that, however. In case you don’t have one, drop in a comment here, I’ll add them to the list myself.

A basic guide to using the software is perhaps in order. The slider on the top jumps through the word list. Press Hit for words you know, this will take you to the next word. Press Miss for the words you don’t – this will show the meaning of the word, and bring up the Next button. Click on it to advance to the next word.

In case you are not sure if the word is what you think it is, click on the word to reveal it’s meaning, and then click on either Hit or Miss depending on whether you were right. Don’t be tempted to simply press Hit now. There’s no point in cheating the software – it’s not a competition, and you’ll be hurting your own revision later on.

Have fun!

¹In hindsight, this is a generic flash card software, which can be used to learn more than just words. You can perhaps suggest a better name for it.

By sandesh247 | Posted in GRE, code, php, programming | Comments (0)

Using javascript to avoid the mouse and page scrolling

June 7, 2009 – 5:29 am

Here’s the problem. It is not very easy to scroll a document when you’re inside an input element. Arrow keys don’t work, and Page Up/Page Down jump in big increments. What if you want to see just a few lines below the current element? Our clients hate to scroll. And they hate having to use the mouse. This just brings the two together.

FScroll is a JQuery plug-in which makes a page scroll to the currently focussed element, keeping it’s position centered with respect to the document. This helps keep a bit of “context” around the currently focussed element – since it is centered, you can see a few elements both above and below the currently focussed element.

Here are the sources. And here’s a page explaining it’s usage in some detail. And oh, it does nested centering too. But it requires that the ‘nesting’ container have a css styling of position : relative (in the demo page, the div enclosing the table is positioned relative). This was not strictly necessary, but it made the coding a bit easier. If you can’t live with the styling restriction, let me know. I’ll try to do what I can.

You may report issues here.

By sandesh247 | Posted in code, jquery, js, programming | Comments (0)

Importing git history into a new svn repository

June 1, 2009 – 10:36 pm

So the management has finally approved your project, and has asked you to start working on it. Heh … little do they know that you’d already been working on it, and have a nice prototype working, and it’s all saved on your local git repository. But your company is not as cool as you are – it has it’s own svn repository, and now you have to import your code into it, history and all.

Here is the git tree, as you have developed it:

Original repostiory structure

.. and your svn repository looks similar to this -

$ svn co <svn repo url>
Checked out revision 0.

$ cd <svnrepo>

$ mkdir tags trunk branches

$ svn add *
A         branches
A         tags
A         trunk

$ svn commit -m "initial directory structure"
Adding         branches
Adding         tags
Adding         trunk

Committed revision 1.

Now you could copy all the files from the git repository into trunk, and commit it. But that is really not the way it should be. For one – no one will know the reason for *anything* in this repository before the big bang. Also, there might have been legitimate reasons for people to branch out from some earlier state of the code, but now no one will even know.

Fortunately, a mail on the kerneltrap archives tells us how we can export a git repository, along with all it’s history, into an svn repository.

(from http://kerneltrap.org/mailarchive/git/2008/10/26/3815034)

From: Björn <B.Steinbrink@…>

…
…

This should do and uses a graft to simplify the process a bit:

Initialize git-svn:

git svn init -s --prefix=svn/ https://svn/svn/SANDBOX/warren/test2

The –prefix gives you remote tracking branches like “svn/trunk” which
is nice because you don’t get ambiguous names if you call your local
branch just “trunk” then. And -s is a shortcut for the standard
trunk/tags/branches layout.

Fetch the initial stuff from svn:

git svn fetch

Now look up the hash of your root commit (should show a single commit):

git rev-list --parents master | grep '^.\{40\}$'

Then get the hash of the empty trunk commit:

git rev-parse svn/trunk

Create the graft:

echo <root-commit-hash> <svn-trunk-commit-hash>  >> .git/info/grafts

Now, “gitk” should show svn/trunk as the first commit on which your
master branch is based.

Make the graft permanent:

git filter-branch -- ^svn/trunk --all

Drop the graft:

rm .git/info/grafts

gitk should still show svn/trunk in the ancestry of master

Linearize your history on top of trunk:

git svn rebase

And now git svn dcommit -n should tell you that it is going to commit
to trunk.

If you check your svn repository log, it will look like this.
SVN log

All the history, nice and linearised for svn.

Keep in mind though, that this method is lossy. All the branches have been linearised, and you can no longer “check them out” in the original git repository. Apart from that, things work just fine, and you can continue to commit in your local git repository, and push to svn as and when needed.

By sandesh247 | Posted in git, svn, tips | Comments (0)

Sights and sounds, in and around Vasai

May 28, 2009 – 12:36 am

This is what population growth, and the resulting competition, can do.

English is a foreign language to most Indians, and yet it seems to be preferred for dispensing information. It’s not uncommon to see a gaffe every now and then.

By sandesh247 | Posted in funny, photos, vasai | Comments (0)

Tuning LINQ performance with Mr. P and Mr. S

May 17, 2009 – 2:22 am

I thought I’d take a second look at the Mr. P and Mr. S problem, which I’d posted more than a couple of years ago. The last time I tried it, I wasn’t successful. I had a strategy to solve it, but somehow I just couldn’t translate it into code.

I’ve been programming a lot with C# lately, and decided to use LINQ to solve the puzzle. Although not very concise, compared to the Python and Haskell solutions out there, it does print out the right answer. After you’ve tried to solve it yourself, you can have a look at my solution here.

There’s something special about LINQ queries. All LINQ queries are deferred, which means that they aren’t executed until they are accessed. Also, they are re-executed when the execution context changes. Say we have a list of numbers, and a query on it like so :

var numbers = new List<int>();
var query =
  from i in numbers
  select i;

The query hasn’t been executed yet. We add a few numbers to the list, and compare the counts of the list and the query.

numbers.Add(0);
numbers.Add(1);
numbers.Add(2);

// 3 elements in list, 3 in the query
Assert.AreEqual(numbers.Count, localDeferredQuery.Count());

The test passes. LINQ queries are “live”, very much like functions. Usually, this is a good thing, as no operation is performed until it is actually needed. However, there are exceptions. For example, I used these three ranges -

public static IEnumerable OddRange(int stop) // returns odd numbers upto "stop"
{
  for (int i = 1; i < stop; i+=2) yield return i;
}

public static IEnumerable EvenRange(int stop) // returns even numbers upto "stop"
{
  for (int i = 2; i < stop; i+=2) yield return i;
}

public static IEnumerable Range(int stop) // returns all numbers upto "stop"
{
  for (int i = 0; i < stop; ++i) yield return i;
}

To define the Deferred() and Immediate() functions below:

public void Deferred()
{
  var all = Range(limit);
  var even = from e in EvenRange(limit) where all.Contains(e) select e;
  var odd = from o in OddRange(limit) where !even.Contains(o) select o;

  var query = from q in odd select q;

  foreach(var i in query) { var j = i+1; }
}

public void Immediate()
{
  var all = Range(limit);
  var even = (from e in EvenRange(limit) where all.Contains(e) select e) .ToArray();
  var odd = (from o in OddRange(limit) where !even.Contains(o) select o) .ToArray();

  var query = (from q in odd select q).ToArray();

  foreach(var i in query) { var j = i+1; }
}

all, even and odd are three sub queries, each using the previous one. The Immediate() function only differs from Differed() due it's forced execution of the subqueries with ToArray(). However, Immediate() performs much better than Deferred(). I knew LINQ operators are actually euphemism for functions, and that iterator blocks are actually exploded by the compiler into a lot of code. But Deferred() was waaaayy slower than Immediate(), and the time taken would increase exponentially with the value of limit. This couldn't be just some extra code.

I posted a query on stackoverflow, and it did not disappoint. It is quite obvious in hindsight. This statement -

var odd = (from o in OddRange(limit) where !even.Contains(o) select o).ToArray();

in deferred mode, turns out to be pretty expensive indeed. It contains a call to even.Contains(o). While in the immediate mode this is an O(n) operation, in deferred mode, the sequence of calls looks like this -

odd --> even -+-> EvenRange()
              |
              +-> all --> Range()

A simple O(n) operation is now O(n³). We can do better than O(n), however, by using a Hashset.

var evenSet = new HashSet(even);
var odd = from o in OddRange(limit)
          where !evenSet.Contains(o) select o; // Contains() is now O(1)

It doesn't get much better than this.

By sandesh247 | Posted in c#, code, programming, tips | Comments (0)

Microblogging on identi.ca

May 10, 2009 – 3:58 am

If my journal template hasn’t changed since this post, you should see a µBlog roll on the sidebar. If you’ve clicked on any of the links, you’d now that those notices (or ‘dents’) come from identi.ca.

identi.ca is a website very similar to twitter, only better. It’s built with the open source laconi.ca project, and has tags and groups too. The killer feature for me is IM support, along with a decent command list. All you have to do is add their bot on google talk, and you can send/receive messages in real -time.

the commands currently supported by the IM bot are:

on - turn on notifications off - turn off notifications help - show this help follow <nickname> - subscribe to user leave <nickname> - unsubscribe from user d <nickname> <text> - direct message to user get <nickname> - get last notice from user whois <nickname> - get profile info on user fav <nickname> - add user's last notice as a 'fave' stats - get your stats stop - same as 'off' quit - same as 'off' sub <nickname> - same as 'follow' unsub <nickname> - same as 'leave' last <nickname> - same as 'get'

identi.ca also supports forwarding dents to twitter, so you wont completely alienate your fans on twitter. However, identi.ca doesn’t pull tweets, so you wont see any @replies from twitter on identi.ca. At least until you can convince your friends to move from twitter.

identi.ca belongs to a larger ecosystem of OpenMicroBlogging software, which have adapted a common standard so that messages between them may be shared. If you use a software that supports OMB, you wont alienate someone just because they happen to like something different (in contrast, the twitter community belongs only on twitter).

Another popular µBlogging site is jaiku, which will support OMB, and go open source soon. If identi.ca is not your cup of tea, or if you happen to like everything Google, jaiku may be for you.

By sandesh247 | Posted in social, web, µBlog | Comments (0)

Good intentions

April 30, 2009 – 2:31 pm

There’s a video about Intentional Software over at MSDN, and it’s definitely one of the more brilliant things to have come out in a while. Most of the times, people who best know how a software should function, are not the ones writing it. That is how people who write software for money, make money – they pitch their ability to convert business requirements into “executables”. With intentional software, everyone does what they do best.

All the places I’ve worked at had tools that made it easy for domain experts to give their inputs, since turnaround time is extremely important for business. Even for personal projects, I’ve toyed with modeling tools and OR mapping frameworks to make my model somewhat independent of the implementation. Never have I seen a tool so comprehensive, though – watching an electrical circuit being modeled as a diagram, along with the impedance and voltages was amazing. This wasn’t just the model being abstracted – it was the whole program, editable as text, diagrams or XML, and easily converted into executable code.

Martin Fowler has quite a lot to say about it too, there isn’t much I can add to it. Open source junkies like me will look for an open source alternative for this, and will find JetBrains’ Meta Programming System. The next few days will be exciting, as I try to evaluate this beast and see whether it fits into any of my current work.

By sandesh247 | Posted in compsci, tools | Comments (0)

On reflecting extension methods in C#

March 27, 2009 – 6:54 am

Extension methods are a great way of adding functionality to existing classes. It almost makes C# similar to ruby/javascript, where none of the classes are “closed” – functionality can be added to them at any point of time.

For example, say we want the method ToTitleCase
to be available to all String objects, and we define an extension method.

namespace MyExtensions
{
    public static class StringExtensions
    {
        public static String ToTitleCase(this String word)
        {
            return word[0].ToString().ToUpper() + word.Substring(1).ToLower();
        }
    }
}

Now, wherever we want to use the method ToTitleCase, we include the namespace MyExtensions, and the following becomes valid C# code :

[TestMethod]
public void TestCall()
{
        Assert.AreEqual("Company", "COMPANY".ToTitleCase());
        Assert.AreEqual("Company", "company".ToTitleCase());
        Assert.AreEqual("Company", "Company".ToTitleCase());
}

However, C# extension methods are simply syntactic sugar. Any extension method calls in source, such as the ones above, are transformed by the compiler into this :

[TestMethod]
public void TestCallClassic()
{
        Assert.AreEqual("Company", StringExtensions.ToTitleCase("COMPANY"));
        Assert.AreEqual("Company", StringExtensions.ToTitleCase("company"));
        Assert.AreEqual("Company", StringExtensions.ToTitleCase("Company"));
}

The extension methods for any given type available to the compiler, but they are compiled as regular static function calls. Feels like cheating, I tell you.

Now what happens when we try to invoke an extension method via reflection?

[TestMethod]
public void TestMethodInfoInTargetClass()
{
    // We won't find the method in String ...
    Assert.IsNull(typeof(String).GetMethod("ToTitleCase"));
}

[TestMethod]
public void TestMethodInfoInDefinigClass()
{
    // But we will find it in StringExtensions.
    Assert.IsNotNull(typeof(StringExtensions).GetMethod("ToTitleCase"));
}

This should be obvious – we aren’t going to find them on the target type – we’ll find them in the class where they are defined.

So, how does this affect us?

Say you’re browsing through some source code, and you see a call like this – myObject.someMethod(). If you need to call the method someMethod() dynamically, you can’t use the type of myObject to reflect it. Instead, you need to know if someMethod() is an extension method, and if it is, you need to reflect it off the class in which it is defined.

That solves the problem when we know which extension method we need to call. If we don’t, and we want to know all the extension methods available for a given type, we can use the attribute ExtensionAttribute. This attribute indicates that a method is an extension method, or that a class or assembly contains extension methods. Given this, we can implement a function that returns all extension methods defined for a given type.

IEnumerable <MethodInfo> GetAllExtensionMethods(Type targetType)
{
    return
        from assembly in AppDomain.CurrentDomain.GetAssemblies()
        where assembly.IsDefined(typeof(ExtensionAttribute), false)
            from type in assembly.GetTypes()
            where type.IsDefined(typeof(ExtensionAttribute), false)
            where type.IsSealed && !type.IsGenericType && !type.IsNested
                from method in type.GetMethods(BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic)
                // this filters extension methods
                where method.IsDefined(typeof(ExtensionAttribute), false)
                where
                    // is it defined on me?
                    targetType == method.GetParameters()[0].ParameterType ||

                    // or on any of my interfaces?
                    targetType.GetInterfaces().Contains(method.GetParameters()[0].ParameterType)

                    // or on any of my base types?
                    targetType.IsSubclassOf(method.GetParameters()[0].ParameterType)
                select method;
}

The above method was inspired by Jon Skeet’s answer on Stack Overflow. It simply improves on it by detecting for interfaces and base types, and looking in all assemblies in the current AppDomain.

Update: Fixed some code up there.

By sandesh247 | Posted in c#, extension, methods, programming | Comments (0)

I flew, and how!

March 23, 2009 – 9:56 am

We were a bit late in our plans, but finally Samson gave the go-ahead.

“ We’ll be taking off from the other end of the beach. See you there in five minutes. ”

The “other” end of the beach was quite some distance away. The wind sock put up to guage the wind velocity was too far to be visible. Barbara and Pascal decided to walk it up, and I took up the risk of pillioning with Joel. We found the wind sock in a couple of minutes – it was barely flying. Not very inspiring, and Joel found it amusing.

“ Don’t worry. If there’s not enough wind for these guys to make you fly, I’ll pull the three of you with my bike. ”

Fat chance.

Samson and Mangesh arrived on a bike soon after, with the winch in tow. Now, Joel is among the healthier people around, and Mangesh did not seem too pleased to see him, but tried to put it across very diplomatically …

“ We’ll need a lighter person for the first ride … let’s not challenge the conditions right away. Around 50 kgs … ? ”

Barbara was still a fair distance away, though. I said I was around 73. So long as it was not Joel, it was apparently ok.

I started putting on the gear. Knee-caps and a helmet. I wonder if they could help me survive a 1000 ft fall. Seemed like a moot point. But I was wrong, they would help me soon.

Barbara and Pascal reached soon after. They were both apparently happy to know they weren’t the first ones on the ride. And along with Joel, they tried to unsettle me a bit.

“ Arre pehla bakra mil gaya inko … tujhse hi poore equipment ki testing hogi. ”

Mangesh did a quick round of the basics with me. Apparently the gliders are very safe, they are designed to quickly recover from most accidents during flight. Each glider has a glide ratio -

“ For a glide ratio of 7:1, if you drew a horizontal of 7ft, and drew a vertical of 1ft downwards, you would be flying along the hypotenuse. ”

He also talked about thermals, wind currents that move upwards due to uneven heating of land. They’d help us gain altitude, but they also bring turbulence. We were on the beach, we weren’t expecting a lot of them.

We were almost ready now. Last minute instructions were doled out. Hands down the sides, within all the hanesses. Run straight, and dont stop. I told Mangesh that it would be a bit awkward to run with both hands tied down, but he said it would only last for 5-6 seconds. As the glider went overhead, the harnesses would loosen. Seemed doable. The wind was ok, not too much of it. Too little, maybe. The winch was attached.

“ 73 kg, NIL wind. Over. ”

Once the conditions were confirmed, we were all set to go. The two men by my side grabbed my arms, and pulled me. I ran, or at least tried to …

The glider gained a bit of height, and my feet were airborne. The gilder came down again, however, and my feet didn’t find the ground. I lost my balance, and …

(somehow, I have a feeling that this will be the most watched video in this post …)

As we fell, Mangesh let the release latch go. The winch separated, and took off with a jerk. Joel didn’t understand what happened, and was a bit concerned.

“ Arre rassi kaise nikal gaya? ”

I got up, and dusted myself. Barbara had commented earlier in the day that I still liked to play in the mud. I got a whole lot of it on myself now. One of the knee caps was left behind, a fair distance behind. You never need these safety precautions, until you do.

We had to try again. The glider was set up behind us, the winch re-attached. We got set again. I was told that it was all up to me – the pilot couldn’t do squat if I wouldn’t pick up speed. As the winch started pulling, so did these guys, and they shouted -

“ Run, run, RUN!!! ”

And run I did.

The whole experience was surreal – I hadn’t felt anything like it before. As the winch pulled on us, and we went higher and higher, I couldn’t help feeling that I was reaching the point of no return – that a fall from this height would be fatal. But those thoughts subsided in a few seconds – the glider was extremely comfortable. Mangesh was pretty cool, though – he must’ve done this million times. He knew the answer, yet he asked -

“ Wonderful, isn’t it? ”

And yes it was. Pascal took along his camera with him when he went up (the third flight of the day, after me and Barbara), and shot this amazing video.

It was wonderful up there. Mangesh kept talking, about the glider, about the winds, and the scene below, but frankly I don’t remember much of it. I was busy enjoying the view.

We really have Samson, and the Space Apple club, to thank for this wonderful experience. If you want to know more about such events in the Vasai-Virar region, you can visit their website.

There are also a few photos of the day on my picasa album.

By sandesh247 | Posted in adventure, paragliding, vasai | Comments (4)