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RE: st: combination of k elements each being 0 or 1


From   "Impavido, Gregorio" <[email protected]>
To   "[email protected]" <[email protected]>
Subject   RE: st: combination of k elements each being 0 or 1
Date   Tue, 4 Mar 2014 20:44:21 +0000

Thank you Robert, Nick and Fernando for all your suggestions which I will study with care. Really appreciated!

Gregorio

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Robert Picard
Sent: Tuesday, March 04, 2014 2:00 PM
To: [email protected]
Subject: Re: st: combination of k elements each being 0 or 1

Here's a non-matrix way of generating the variables using the equivalent of -cross-

clear
set obs 2
gen v1 = _n - 1

local k 5
forvalues i = 2/`k' {
expand 2
local j = `i' - 1
bys v1-v`j': gen v`i' = _n - 1
}

Robert

On Tue, Mar 4, 2014 at 1:45 PM, Nick Cox <[email protected]> wrote:
> Following Fernando's insight, this is possible with the -egen- 
> function -base()- from -egenmore- (SSC). The help for -egenmore- 
> spells out ways to unpack the string variable into separate variables.
>
> . clear
>
> . local x 8
>
> . set obs `=2^`x''
> obs was 0, now 256
>
> . gen dec = _n - 1
>
> . egen bin = base(dec)
>
> . l if inrange(_n, 1,4) | inrange(_n, 253,256) , sep(4)
>
>      +----------------+
>      | dec        bin |
>      |----------------|
>   1. |   0   00000000 |
>   2. |   1   00000001 |
>   3. |   2   00000010 |
>   4. |   3   00000011 |
>      |----------------|
> 253. | 252   11111100 |
> 254. | 253   11111101 |
> 255. | 254   11111110 |
> 256. | 255   11111111 |
>      +----------------+
>
> Nick
> [email protected]
>
>
> On 4 March 2014 18:30, Fernando Rios Avila <[email protected]> wrote:
>> Hi Gregorio,
>> I do have a suggestion for the generalization of your algorithm. What 
>> you are doing can be thought as the transformation from a number from 
>> base 10 to base 2 It could go something like: (using your base code).
>> clear
>> local x 8
>> local n=2^`x'
>> set obs `n'
>> gen v0=""
>> forvalues i=1/`n' {
>> local n2=`i'-1
>> inbase 2 `n2'
>> return list
>> replace v0=r(base) in `i'
>> }
>>
>> destring v0, replace
>>
>> forvalues i=1/`x' {
>> gen v`i'=mod(v0,10)
>> replace v0=int(v0/10)
>> }
>>
>> HTH
>> Fernando
>>
>> On Tue, Mar 4, 2014 at 12:48 PM, Impavido, Gregorio <[email protected]> wrote:
>>> Hello.
>>>
>>> I would like to define a matrix (2^k x k) with all possible combinations of k elements each being 0 or 1.  The code below produces what I want for k = 5 and can be modified for different values of k. My questions are:
>>>
>>> - Is there a matrix function in STATA or MATA that generalizes the code below for variable k?
>>> - If not, does anybody have suggestions on how to generalize the loop for variable k?
>>>
>>> Thank you in advance for your help
>>> Gregorio
>>>
>>>
>>>
>>> ******* begin example
>>> clear
>>> set more off
>>> local x 5
>>>
>>> local n = 2^`x'
>>> set obs `n'
>>>
>>> forvalues i = 1/`x' {
>>> gen v`i' = .
>>> }
>>>
>>> * set trace on
>>> local j = 1
>>> while `j' < `n' {
>>> forvalues i1 = 0/1 {
>>>         forvalues i2 = 0/1 {
>>>                 forvalues i3 = 0/1 {
>>>                         forvalues i4 = 0/1 {
>>>                                 forvalues i5 = 0/1 {
>>>                                         forvalues l = 1/`x' {
>>>                                                 replace v`l' = `i`l'' in `j'
>>>                                                 }
>>>                                                 local j = `j' + 1
>>>                                         }
>>>                                 }
>>>                         }
>>>                 }
>>>         }
>>> }
>>> ******* end example
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