# st: RE: Extracting Matrices from dataset

 From "Nick Cox" To Subject st: RE: Extracting Matrices from dataset Date Mon, 20 Aug 2007 13:36:10 +0100

```Two earlier versions of this posting appeared yesterday.
They referred to Mata.

As with other concurrent threads, questions that are
not precise, or even stated, or which seem to be easily
answerable from the documentation tend to get little or no
response.

1. Functions to read Stata variables into Mata are
well documented in the Mata documentation. You shouldn't
need to write any new functions. See -help m4_stata-.

2. As you don't state what you want to do with these matrices,
it isn't clear whether your inclination to use Mata is

Nick
n.j.cox@durham.ac.uk

> I wish to extract matrices based on a grouping varible in the dataset.
> Consider the following example suppose I have three groups (1,2 and 3)
> entered in "gr" variable
>
> m	v1	v2 	v3	gr
> **********************************
> 23	1	2	3	1
> 11	3	1	2	1
> 23	2	2	1	1
>
> 25	1	2	3	2
> 23	2	1	2	2
> 28	3	3	1	2
>
> 2	1	1	2	3
> 3	1	3	1	3
> 1	2	1	2	3
>
> and i wish to extract three vectors say
>
> 	m_1=(23,11,23)
>
> 		m_2=(25,23,28)
>
> 			m_3=(2,3,1)
>
> or I wish to extract three matrices say
>
> v_1=(1,2,3\3,1,2\2,2,1)
>
> 	v_2=(1,2,3\2,1,2\3,3,1)
>
> 		v_3=(1,1,2\1,3,1\2,1,2)
>
>
> similary if i have four groups then generated matrices or vectors
> should be four and if i have five groups then the generated matrices
> should be five and so on.

*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/
```