Every time I look at the examples page of D3, I’m simply go…

@mbostock has transformed how visualizations are created for web.

Today I learnt how to use svg markers with D3. I was using force layout to analyze graphs, just like this example. But I wanted a directed graph!

Later, I came across another example which had direction. I was happy because a ready-made solution solved the problem. But soon I ran into problem as I wanted a custom tree like structure with every path being directed i.e I wanted the arrow markers at the end of each path.

I went back to the ready-made solution and had a look at the part of code which was generating the arrows.

// build the arrow.
svg.append("svg:defs").selectAll("marker")
// Different link/path types can be defined here
.data(["end"])      
// This section adds in the arrows
//this makes the id as 'end', coming from data
.attr("id", String)

I always wanted to setup a media server at home for the following reasons:

1. Reduce redundancy - having multiple copies of media for different devices like phone, tablet, smart TV etc
2. Ease of use - no need to copy files to and from devices to play media (mostly Floyd and movies)
3. One stop shop with transmission integration - download files on rpi and they appear on the media server

The easiest solution was to turn my RaspberryPi into a DLNA server. For this I required to a few basic packages and had to configure each.

It was a bit hard to find all of them in a single post and hence I’m writing this post.

Packages required

• samba
• nginx (for transmission)
• nfs
• ntfs (optional, to support ntfs file system)
• transmission-daemon

• minidlna

  sudo apt-get install samba samba-common-bin
  sudo apt-get install nginx
  sudo apt-get install nfs-kernel-server nfs-common portmap
  sudo apt-get install

  ...

PostgreSQL has out of box support for text search.

Assume we have a table of documents:

CREATE TABLE documents
(
  id serial NOT NULL,
  doc text
)

INSERT INTO documents(doc)
VALUES ("Lorem ipsum .....");

INSERT INTO documents(doc)
VALUES ("Quick brown fox .....");

------------------------------------
id       | doc
------------------------------------
0        | "Lorem ipsum ....."
1        | "Quick brown fox ..."

A simple text search is a basic requirement in any system. This can be done using tsvector and tsquery types in PostgreSQL.

[tsvector](www.postgresql.org/docs/9.1/static/datatype-textsearch.html) gives us the list of lexemes for any given text.

[tsquery](www.postgresql.org/docs/9.1/static/datatype-textsearch.html) helps facilitate the search by creating lexemes for search terms, combine search terms / lexemes and compare with tsvector for result.

The to_tsvector...

I had zero knowledge about this topic but wanted to explore. Took Large Scale Hierarchical
Text Classification (LSHTC) as my MS project, so that I have a good scenario to start Machine
Learning

The first thing I wanted to know was the format of data provided by LSHTC. Turned out that it
was SVM format. The training data and test data had the following format

label,label,label… feature:value feature:value

The label indicates the category the document belongs to.

The feature:value vector represents a word and its weight (TF) in the document.

Choice of programming language

Had to make a choice between Java and Python

I chose Python for the following reasons:

1. Huge set of Machine Learning libraries - given that I was a beginner, this made a lot of impact. More libraries, more documentation, more examples => more experiments and better understanding
2. Most of the Machine Learning this...

Database trigger is an event that can occur after or before a statement is executed or a row is modified / inserted / deleted.
This can be used to perform any task before or after certain occurrence of an event in the database.

I was curious about this concept from a very long time and wanted to check it out.

I wanted to try an automation by creating a trigger function.

Trigger function in PostgreSQL is a kind of function to which special variables are passed - NEW, OLD etc. More on trigger functions - here

NEW - variable sent to trigger function when the trigger is INSERT / UPDATE. This variable will contain the new row to be inserted / updated

OLD - variable sent to trigger function when the trigger is DELETE. This variable will contain the row to be deleted

To try out trigger functions I created three tables posts, groups and user_posts

I wanted to try an insert automation -...