Convert Different Audio In Command Line in Ubuntu

Converting different audio formats in Ubuntu is quite an easy task. Just start Soundconverter, or first install it, if you don't have.

sudo apt-get install soundconverter

But I needed to do it in command line. Soundconverter can do it either. (What a good boy!) But you just need to know the mime-type of the output file (simply adding the desired suffix doesn't work). For example, to convert "my_favourite mp3" to wav you can use:

soundconverter -b -m audio/x-wav -s .wav my_favourite.mp3

See the full list of mime types.

For the available options see

soundconverter -h

or

man soundconverter

Ruby Shoes

I wanted to try ruby Shoes already long ago, but just didn't know what to start with. Until I found a quiteuseful article about making a game on ruby shoes. I tried it and it was unexpectedly easy. Here are some my subjective thoughts about it.

Good things:

It is very easy to study.

One can begin writing using shoes quite quickly and straightforward. No big manuals or hardly understandable api and howtos.

It is cute. :)

Yes, I really liked it. Different objects are created very easy, such as:

Shoes.app { button("Click me!") { alert("Good job.") } }

You also can draw with provided rect, oval or even arrow methods or import an image as a background. Motion ability is also provided:

Shoes.app do #A star that moves after the mouse pointer.
  @shape = star :points => 5
  motion do |left, top|
    @shape.move left, top
  end
end

Unfortunately there were also some disadvantages:

The whole Shoes application should be in Shoes.app block.

Seem to me to be a little bit uncomfortable.

You have to pass everywhere app variable that denotes the Shoes application.

Well, not just everywhere... But if you create your own class, which objects have to be drawn you also have to pass the application variable, or make it global, which is not really good pattern.

class RedRect

  def initialize( app )
    app.fill red
    app.rect :left => 10, :top => 10, :width => 40 
  end
end

Shoes.app do
  RedRect.new( self )
end

Pity, but it is slow.

The resulting snake in the game responds in about 2 seconds. It is a long period of time, especially on higher levels with higher speed.

In conclusion the authors' words about Shoes are right:"Shoes is a tiny graphics toolkit, designed for beginners". It can be used to create quickly a small application, where speed is not essential.

Access DOM Element Within IFrame

Suppose we have a html page with frame or iframe in it and we need to get an element in it. Simple

document.getElementById("myElement");

will not find it, as it is searched only in the main page, where the frame is set. What we should do, is to find the frame first and then look for needed element in the right frame.

frame = document.getElementById("myFrame"); 
frame.contentWindow.getElementById("myElement");

Concatenate Strings On Group By In Sql

Imagine we have the following table.

CREATE TABLE MyTable (id int, name varchar, value int);

INSERT INTO MyTable (id,name,value) VALUES (1, 'Hello', 4);
INSERT INTO MyTable (id,name,value) VALUES (1, 'World', 8);
INSERT INTO MyTable (id,name,value) VALUES (5, 'Great!', 9);

The result we would like to acquire is:

| id |   name_values    |
+----+------------------+
|  1 | Hello:4; World:8 |
|  5 | Great!:9         |

Names and values are concatenated into strings and grouped by id. We need an aggregate function, that concatenates strings for that. Here are some solutions for different sql databases.

MySql

This case is most easy one. Lucky users already have the GROUP_CONCAT(expr) function. This query should give the answer.

SELECT id, GROUP_CONCAT(name + ':' + value SEPARATOR '; ') AS name_values FROM MyTable GROUP BY id;

PostgreSql

The solution here is a bit more difficult, but nevertheless easy enough. We need to create our own aggregate function and use it in our query.

CREATE AGGREGATE aggr_textcat(
  basetype    = text,
  sfunc       = textcat,
  stype       = text,
  initcond    = ''
);

SELECT id, substring(aggr_textcat(', ' || name || ':' || value) from 2) AS name_values FROM MyTable GROUP BY id;

Here we used already existing function to concatenate text fields textcat, but we could write our own.

MsSql

Since version 2005 it became also possible to write your own aggregate function in MsSql, but here I provide another solution using inner select and xml path.

SELECT id, SUBSTRING((SELECT '; ' + name + ':' + CAST(value AS varchar(MAX)) 
FROM MyTable WHERE (id = Results.id) FOR XML PATH ('')),3,9999) AS name_values
FROM MyTable Results
GROUP BY id

Insert Large Amount Of Rows Into PostgreSQL

Inserting large amount of data into postgres database may take a lot of time, if you use INSERT command. Consider better COPY command, though it is not so flexible.

COPY my_table_name(int_column, string_column, bytea_column) from stdin;
1    THISisSTRING    \\001\\017\\044
2    THISisSTRING2   \\001\\017\\062
3    THISisSTRING3   \\001\\017\\102

The default delimiter is tab (\t).

To acquire the right format in 1 particular case, you can fill database with some values using INSERT command and dump database with pg_dump. The resulting file will contain the right COPY syntax.

Ajax With InnerHTML()

InnerHTML is not a standard, but it is more useful comparing to working with DOM with such functions as createElement and/or appendChild. But there is a problem with it: if you need further to handle the new added data (to refer new elements, to change/add their attributes), innerHTML is not good at all, as innerHTML simply visually adds new elements, but it does not really insert them in the DOM structure of the document. Attempting to do a document.getElementById() on a tag inside of code that was added using innerHTML just doesn't work. At least it didn't work for me in Firefox 3.

The folowing code can be accepted as the workaround.

var newDiv = document.createElement("div");//create new div
newDiv.innerHTML = xhr.responseText;//add response into new div
var container = document.getElementById("container");//find place where the response should be placed to
container.parentNode.insertBefore(newDiv, container);//add new div before the container
newDiv.parentNode.removeChild(container);//remove container

This way we get the same resulting document, but we can further work with DOM.

Master Degree Acquired

Yes, at last. Now I am the Master of the Information Technology :) Sounds good!

Microsoft Excel 2007 Problems

It is a must read, if you want to know what problems you may encounter, when exporting to excel 2007: "Microsoft Office XML formats ? Defective by design"

Array To String

Oh, how I hate String.join(string, string[]) in mscorlib. And it is because of string[] argument. Why couldn't they make it accept array of objects and, before joining, cast every object with ToString() method?

Had to make it myself:

public string ListJoin<T>(string separator, T[] objs)//C# v3
{
  return string.Join(separator, Array.ConvertAll(objs, item => item.ToString()));
}

public string ListJoin<T>(string separator, T[] objs)//C# v2
{
  return string.Join(separator, Array.ConvertAll<T,string>(value, new Converter<T,string>(delegate(T i){return i.ToString();})));
}

Export String Values To Excel 2007

If you encounter a following error, while exporting to Excel 2007 (.xlsx)

Errors were detected in file MyFileName.xlsx. Repaired Records: Cell information from /xl/worksheets/sheet1.xml part

then, probably, you are exporting string values in wrong format. The right structure in this case is

<sheetData>
  <row>
   <c>
     <v>99999</v>
   </c>
   <c t="inlineStr">
     <is>
       <t>My Text</t>
     </is>
   </c>
  </row>
</sheetData>

Note, that there is no <v> tag in <c> as it should be with numbers. Instead you have to make an inline string (<is>) tag and put text (<t>) tag with needed text in it. Do not forget to add the t="inlineStr" attribute to <c> tag.

More info can be found developer:network.