Finally ...

... I had someone from China mistake me for a Chinese person. This, after years of being told that I look like Chinese person while in India. Inevitable, I guess.

Cabbage and rice tastes great!

Or maybe it is the hunger speaking. I didn't have breakfast - skipped directly to lunch.

This was a day after I visited NYC. Thanks to Shrikanth, I have some photos from my university now.

Have a look. NYC photographs will follow soon.

Edit: Let's try a slideshow -

The weaker sex?

From http://esr.ibiblio.org/?p=2118:

... women, in general, are not willing to eat the kind of shit that men will swallow to work in this field. Now let’s talk about death marches, mandatory uncompensated overtime, the beeper on the belt, and having no life. Men accept these conditions because they’re easily hooked into a monomaniacal, warrior-ethic way of thinking in which achievement of the mission is everything. Women, not so much. Much sooner than a man would, a woman will ask: "Why, exactly, am I putting up with this?"

... if we really want to fix the problem of too few women in computing, we need to ask some much harder questions about how the field treats everyone in it.

More like the wiser one.

Using unicode to annotate emails

I have been using unicode characters like ★, ✘, ✔, ⚠ to annotate my gmail labels. I used it today to mark the subject of one of my mails as a high-priority mail. Wonder if it'll work.

Using javascript to avoid the mouse and page scrolling

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.

Importing git history into a new svn repository

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:



.. 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.


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.

Sights and sounds, in and around Vasai

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.

Do you see me?

Updating my profile picture isn't an easy task anymore. There are many sites where I own a profile, and I have to look just right on each one of them.

As of now, these are the places you can see my shiny new profile picture:

• http://sandesh247.com


• http://www.google.com/profiles/sandesh247


• http://www.linkedin.com/in/sandesh247


• http://identi.ca/sandesh247/


• http://www.facebook.com/profile.php?id=543752933


• http://www.goodreads.com/sandesh247


• http://www.last.fm/user/sandesh247


• http://friendfeed.com/sandesh247


• http://www.orkut.co.in/Main#FullProfile.aspx?uid=6964782234814101571


• http://www.gravatar.com/avatar/f37a7393ce728b072aca55535f759e9f (all gravatar enabled websites)


• http://twitter.com/sandesh247

 
Phew. I hope that covers them all.

P.S. Last.fm and Twitter aren't playing nice right now. I guess I have to keep trying.

Tuning LINQ performance with Mr. P and Mr. S

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.

Microblogging on identi.ca

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.