format a matrix

[Trung BUI]

Hello user,

For example, I have a matrix A = (1.12132, 3.036563, 3.2323 \ 2.60223, 3.710003, 4.5343342 ).

How could I format the matrix A round every element with 2 decimal) as follows:
A = (1.12, 3.04, 3.23 \ 2.60, 3.71, 4.53 ).

Thanks a lot in advance.

[Nick Cox]

Formatting a matrix is a matter of display only; stored values are not affected.

If you want a record of that matrix with just 2 decimal places, that is a string conversion and best accomplished in Mata.

Rounding numerically to 2 decimal places could at best be an approximation given precision issues.

.  matrix A = (1.12132, 3.036563, 3.2323 \ 2.60223, 3.710003, 4.5343342 )

. mat li A, format(%3.2f)

A[2,3]
      c1    c2    c3
r1  1.12  3.04  3.23
r2  2.60  3.71  4.53

. mata
------------------------------------------------- mata (type end to exit) ------
: A = st_matrix("A")

: strofreal(A, "%3.2f")
          1      2      3
    +----------------------+
  1 |  1.12   3.04   3.23  |
  2 |  2.60   3.71   4.53  |
    +----------------------+

[Trung BUI]

Dear Cox,

I used your mata code in an attempt to round the matrix A to 2 decimal. However, it seems that the matrix A is unchanged.

Could you provide the mata code for this purpose?

[Nick Cox]

(My first name is Nick; Cox is the family name; using the first is conventional here, please, if you wish to use names at all.)

My Mata code doesn't purport to change the matrix. It just shows a string representation in Mata.

You should follow entries in

 
search precision

to see that the desire here is problematic. But as you press the point, this is a way to give you what I think you think you want.

. matrix A = (1.12132, 3.036563, 3.2323 \ 2.60223, 3.710003, 4.5343342 )

. matmap A B, map(round(@, 0.01))

. mat li B

B[2,3]
      c1    c2    c3
r1  1.12  3.04  3.23
r2   2.6  3.71  4.53

. mat li B, format(%21.18f)

B[2,3]
                      c1                    c2                    c3
r1  1.120000000000000100  3.040000000000000000  3.230000000000000000
r2  2.600000000000000100  3.710000000000000000  4.530000000000000200

Here matmap is from SSC. Note that the last example underlines that you can only ever get 2 decimal places as an approximation.

[Clyde Schechter]

And if you don't want to change the matrix, and just want to display it to 2 decimal places:

matrix list A, format(%3.2f)