[Tutor] sorting a list of dictionaries

[Gooch, John]

I am working on a dictionary sorting problem just like the one in the email
thread at the bottom of this message. My question about their solution is:
In these lines:
	lst.sort(lambda m, n: cmp(m.get(field), n.get(field)))
	where field is either 'name' or 'size'.

What is "n:" and what is "lambda m" ? 


Thank You, 

John A. Gooch

-----Original Message-----
From: sigurd at 12move.de [mailto:sigurd at 12move.de] 
Sent: Thursday, December 09, 2004 12:19 PM
To: tutor at python.org
Subject: Re: [Tutor] sorting a list of dictionaries


On  9 Dez 2004, ljholish at speakeasy.net wrote:

> I have a list of dictionaries, each representing info about a file, 
> something like:
>
> [{'name':'foo.txt','size':35}, {'name':'bar.txt','size':35}, ...]
>
> I want to present a sorted list of all the files' data, sorting on the 
> keys 'name' or 'size'. The file 'name' s should be unique (I'm hoping) 
> across all the dictionaries. Can someone point me towards an efficient 
> solution for accomplishing the sort? (The list has 1000s of files).

That's easy to achieve, since sort takes a custom sort function as optional
argument.  Now you need only a function which takes the values of the fileds
and compares them.

E.g.

lst.sort(lambda m, n: cmp(m.get(field), n.get(field)))
where field is either 'name' or 'size'.

As a function:

def sort_it (lst, field):
    lst.sort(lambda m, n: cmp(m.get(field), n.get(field)))


   Karl
-- 
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