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I am trying to write a command that ereturns a scalar that is percentage rounded to 2 decimal places. The percentage can be negative or positive, with unknown number of digits before the decimal point.

Here's MRE that shows the problem I am having.

#delimit;

capture program drop my_note;
program my_note, eclass;
    local my_x: display %-9.2f 92.23999999999999;
    ereturn scalar my_x = `my_x';
end;

ereturn clear;
my_note;
ereturn list;

display %-9.2f 92.23999999999999;
display 92.23999999999999;

I am puzzled why display seems to do the right thing (turn 92.23999999999999 to 92.24, though regardless of format), but that e(my_x) does not seem to inherit that format.

dimitriy
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    Every variable has a display format, as you know, which you can change. The format is in a strong sense a property of the variable. When you use a display format on a local macro the local neither sees nor remembers the format: it is the contents of the macro, once evaluated, that are being displayed. – Nick Cox Jan 27 '20 at 07:48
  • Your choice is between returning a local macro with formatted contents, a string scalar ditto, and a numeric scalar which you display as desired. – Nick Cox Jan 27 '20 at 08:17
  • @NickCox is right. Formatting and rounding a variable are two separate things. –  Jan 27 '20 at 12:45

1 Answers1

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When you create your scalar you copy the value of the local `my_x'. That value is still 92.23999999999999 as : display is not changing the underlying data, only how it is displayed. Think of it as the data in 5.00e+2 and 500 is the same, it is just how that value is shown that differs.

You need to use strings to work with how the value is displayed. However, there are two issues with strings in your code example.

  1. While scalars normally can hold both strings and numeric values, returned scalars can not hold strings (don't ask me why). Would it be possible to return a local instead?

  2. In %-9.2f you specify that the display format to be 9 characters long so your scalar will be e(my_x) : "92.24 ". You can adjust %-9.2f, but since you are now working with strings you can remove excessive spaces using the trim() function.

Try the code below and see if that works given the context of this function. If not tell us more about what you are about to do.

#delimit;

capture program drop my_note;
program my_note, eclass;
    local my_x: display %-9.2f 92.23999999999999;
    ereturn local my_x = trim("`my_x'");
end;

ereturn clear;
my_note;
ereturn list;
TheIceBear
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