[BangPypers] list to dictionary problem

[Senthil Kumaran]

On Tue, Jun 22, 2010 at 02:23:43AM -0000, Vikram  wrote:
> Suppose i have this list:
> 
> >>> a = [['cat',2],['cat',5],['cat',9],['dog',6]]
> >>> a
> [['cat', 2], ['cat', 5], ['cat', 9], ['dog', 6]]
> 
> Now, there is a nice way to obtain the value 9.

This is using the side effect of dict creation. Not a nice way. :)
The rule is that last value with the same key will be over-written. If
you use it any of your larger applications, the next person who is
going to read your code will likely be frustrated.

> >>> z = dict(a)
> >>> z
> {'dog': 6, 'cat': 9}
> 
> Is there any elegant way to extract the value 2? (Value corresponding to the first occurence of 'cat' in the 2-D list

Nope, it is not elegant.
The best way is to be explicit. Loop over list, create a dict with the
value as the list of values the original list and then deal with the
list value as you would like to. First element is "elegantly" [0] and
the last element is "nicely" [-1]. :)

-- 
Senthil

We don't understand the software, and sometimes we don't understand the
hardware, but we can *___see* the blinking lights!