Re: finding keys in a table

[Romulo <romulo@...>]

For performance I'd just intialize all characters to zero:

local count = {}

for i = 0, 255 do
    count[ string.char( i ) ] = 0
end

for c in string.gmatch( io.read( "*a" ), "." ) do
    count[ c ] = count[ c ] + 1
end

-- And to iterate over them:

for i = 0, 255 do
    local c = string.char( i )
    if count[ c ] > 0 then
        print( c, count[ c ] )
    end
end

-- Or just remove the zeroes

for i = 255, 0, -1 do
    local c = string.char( i )
    if count[ c ] == 0 then
        count[ c ] = nil
    end
end
table.foreach( count, print )


*not tested* ;)

--rb

On Thu, Feb 21, 2008 at 11:24 AM, Jelle Huisman <jelle@jhnet.nl> wrote:
> Hello,
>
>  I need a frequency list of all characters in a text file and I try to
>  use a table for this but I'm not totally sure if this is the best way to
>  solve my problem. Anyway I setup a table "count" with the characters as
>  key and a counter as value. When I iterate over my data I want to:
>  (1) lookup if the current character already exists as a key in the table.
>  (2a) If it does exist I increment the value for key currentchar with 1
>  (2b) else I add a new entry: currentchar=1
>  (3) Later I sort the table and print my freq.list.
>
>  The two questions I have are: is this the best/most efficient/fastest
>  way to do this?
>  Second: How do I check if a key exists? (I don't think I can use an
>  inverted table because I'll end up with duplicate keys, or not?)
>
>  Thanks for some advice,
>
>  Jelle
>
>