Re: st: RE: mata: columns of different eltypes in a transmorphic matrix

[Nick Cox <njcoxstata@gmail.com>]

Naturally, you do often need to combine numeric and string, and the
answer is that strings can include numeric characters, but not vice
versa. So, we can do things like this:

sysuse auto

In Mata:

: make = st_sdata(., "make", "foreign")

: make
                     1
     +------------------+
   1 |       Audi 5000  |
   2 |        Audi Fox  |
   3 |        BMW 320i  |
   4 |      Datsun 200  |
   5 |      Datsun 210  |
   6 |      Datsun 510  |
   7 |      Datsun 810  |
   8 |     Fiat Strada  |
   9 |    Honda Accord  |
  10 |     Honda Civic  |
  11 |       Mazda GLC  |
  12 |     Peugeot 604  |
  13 |  Renault Le Car  |
  14 |          Subaru  |
  15 |   Toyota Celica  |
  16 |  Toyota Corolla  |
  17 |   Toyota Corona  |
  18 |       VW Dasher  |
  19 |       VW Diesel  |
  20 |       VW Rabbit  |
  21 |     VW Scirocco  |
  22 |       Volvo 260  |
     +------------------+

: price  = st_data(., "price", "foreign")

: make, strofreal(price, "%2.0f")
                     1                2
     +-----------------------------------+
   1 |       Audi 5000             9690  |
   2 |        Audi Fox             6295  |
   3 |        BMW 320i             9735  |
   4 |      Datsun 200             6229  |
   5 |      Datsun 210             4589  |
   6 |      Datsun 510             5079  |
   7 |      Datsun 810             8129  |
   8 |     Fiat Strada             4296  |
   9 |    Honda Accord             5799  |
  10 |     Honda Civic             4499  |
  11 |       Mazda GLC             3995  |
  12 |     Peugeot 604            12990  |
  13 |  Renault Le Car             3895  |
  14 |          Subaru             3798  |
  15 |   Toyota Celica             5899  |
  16 |  Toyota Corolla             3748  |
  17 |   Toyota Corona             5719  |
  18 |       VW Dasher             7140  |
  19 |       VW Diesel             5397  |
  20 |       VW Rabbit             4697  |
  21 |     VW Scirocco             6850  |
  22 |       Volvo 260            11995  |
     +-----------------------------------+
Nick
njcoxstata@gmail.com


On 10 October 2013 13:27, Joseph Coveney <stajc2@gmail.com> wrote:
> Nick Cox wrote:
>
> This is an excellent answer, but one simple point seems submerged. An
> elementary strategy is to put numeric variables in a numeric matrix
> and string variables in a string matrix.  I've often done that in Mata
> programs, and never yet felt the need for structs, pointers, and so
> forth.
>
> --------------------------------------------------------------------------------
>
> I agree.   I'm not sure what László's needs are for keeping Stata dataset string
> and numeric data in sync in a single location in Mata.  Perhaps, if he'd like to
> elaborate, someone on the list could offer suggestions that don't entail structs
> or pointer vectors, List or Array classes, and the like.
>
> As you could see from my example, taking the long way round involves additional
> programming steps that in turn give rise to opportunities for logical errors,
> such as -select(X, missing(X[1,]))- instead of -select(X, !missing(X[1,]))-, and
> syntax errors, such as -PointerVector = (A, B)- instead of -PointerVector = &A,
> &B-, among others that I haven't noticed yet.
>
> Joseph Coveney
>
>
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