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From |
wgould@stata.com (William Gould, Stata) |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Determining the width of a formatted value |

Date |
Mon, 07 Apr 2003 09:52:26 -0500 |

Bryan Sayer <BSayer@s-3.com> asked about how the width <w> is treated in the %<w>.<d>g and %<w>.<d>gc display formats. For instance, . display %12.0gc 12345678 results in ----+----1-- 12,345,678 yet . display %12.0gc 123456789 results in ----+----1-- 123456789 when ----+----1-- 123,456,789 looks possible to Bryan. The answer is that %g and %gc puts aside two of the positions for a sign and for a decimal point in case either should be necessary. By this logic, a %12.0gc format has 12-2=10 positions for digits and commas. Obviously, the code could be written to make use of the positions for the sign and decimal point when they are not necessary, but setting aside the two positions is how the code works right now and it is not on our list to change that. Another subject --------------- What follows is unrelated to Bryan's query. I would like to mention the new-to-Stata-8 %<w>.<d>g and %<w>.<d>gc formats when <d> is greater than 0. I am not certain many of you noticed the change. %12.0g, as you know, shows a number in field of width 12. That number is displayed in such away as to show as many of its digits as possible. ----+----1----+----2 3.141592654 <- display %12.0g _pi 31.41592654 <- display %12.0g _pi*10 314159.2654 <- display %12.0g _pi*10^5 314159265.4 <- display %12.0g _pi*10^8 3141592654 <- display %12.0g _pi*10^9 3.14159e+10 <- display %12.0g _pi*10^10 3.141592654 <- display %12.0g _pi .3141592654 <- display %12.0g _pi*10^(-1) .0003141593 <- display %12.0g _pi*10^(-4) .0000314159 <- display %12.0g _pi*10^(-5) 3.14159e-06 <- display %12.0g _pi*10^(-6) I want to draw you attention especially to that last two lines: .0000314159 3.14159e-06 Note how smart is %12.0g. It could have displayed _pi*10^(-6) as .0000031415 but it knew that, if it switched to %e format, it could display an extra digit, and so it did. That's the purpose of the %g format: to show as many digits as possible within the specified width. New to Stata 8, you can specify the maximum number of digits you want, which you specify as the <d> in %<w>.<d>g: ----+----1----+----2 3.142 <- display %12.4g _pi 31.42 <- display %12.4g _pi*10 3142 <- display %12.4g _pi*10^3 314159 <- display %12.4g _pi*10^5 31415927 <- display %12.4g _pi*10^7 3141592654 <- display %12.4g _pi*10^9 3.142e+10 <- display %12.4g _pi*10^10 3.142 <- display %12.4g _pi .3142 <- display %12.4g _pi*10^(-1) .0003142 <- display %12.4g _pi*10^(-4) .00003142 <- display %12.4g _pi*10^(-5) 3.1412e-06 <- display %12.4g _pi*10^(-6) %12.4g is almost a 4-significant digit format, the exceptions being 314159 <- display %12.4g _pi*10^5 31415927 <- display %12.4g _pi*10^7 3141592654 <- display %12.4g _pi*10^9 To show those with 4 digits would have required either going to %e format: 3.1412e+05 3.1412e+07 3.1412e+09 or rounding and padding the numbers with zeros 314200 31420000 3142000000 The %w.dg, d>0, format assumes you do not want either of those solutions. If you wanted the %e format, you can use the %e format at the outset. We thought about implementing the round-and-pad solution, but came to the conclusion that researchers don't want that. As long as digits are going to be displayed, one might as well put the actual digit in each position. If there is an interest in the round-and-pad solution, we would be willing to implement a %G format to go along with %g. -- Bill wgould@stata.com * * 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/

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