[Jprogramming] /. in inverted tables

[Roger Hui]

tindexof  =: i.&>~@[ i.&|: i.&>
tkey=: 1 : '<@tindexof~@[ u/.&.> ]'



----- Original Message -----
From: "Sherlock, Ric" <R.G.Sherlock at massey.ac.nz>
Date: Thursday, September 27, 2007 18:16
Subject: [Jprogramming] /.  in inverted tables
To: Programming forum <programming at jsoftware.com>

> I'm investigating working with data stored in inverted tables.
> <http://www.jsoftware.com/jwiki/Essays/Inverted_Table>
> 
> Some example data:
> hdr=: ;: 'ID DOB Sex Nat Height Weight Arrests'
> x0=: 'ID',"1 ];._1 ' ',": 10000+ 40 ?.@$ 4
> x1=: 1998+ 40 ?.@$ 4
> x2=: (40 ?.@$ 2){ >'Female';'Male'
> x3=: (40 ?.@$ 3){ >'NZ';'US';'CH'
> x4=: 1.2 +  1 * (40?.@$ 0)
> x5=:  60 + 12 * (40?.@$ 0)
> x6=: 40 ?.@$ 6
> invtble=: x0;x1;x2;x3;x4;x5;x6
> 
> I came up with the following to give the frequency of each 
> unique rows
> in an inverted table:
> tfreq=: #/.~@:|:@:(i.&>)~
> 
> key=: 1 3 2{invtble
> ,.each tfreq key
> 
> The following verb makes a frequency table:
> tfreqtble=: [: tsort tnub , <@:tfreq
> 
> ,.each tfreqtble key
> 
> Or a more generalised version
> tkeytble=: [: tsort ([: tnub [) , [: boxopen ]
> 
> ,.each key tkeytble tfreq key
> 
> And I can calculate say the sums of data columns by the set of key
> columns e.g.
> tkeysum=: ] +//.&.>~ <@:tindexof~@:[
> 
> dat=: 4 5 6{invtble
> ,.each key tkeysum dat
> 
> But what I think I really want is a verb tkey, that does what /. does,
> but on inverted tables.
> Then instead of defining tkeysum, tkeymin, tkeymax ..., I could 
> do this:
>   key +/tkey  dat
>   key <./tkey dat
>   key >./tkey dat
>   ...
> Or in a sorted table:
> ,.each  key tkeytble key +/tkey dat
> 
> Any pointers or other approaches to consider gratefully accepted!