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Re: st: gsort issue
Or even,
set missing smallest
?
Jeph Herrin wrote:
I'm with Fred & Nick. After using Stata exclusively for
over a decade, I still find that my intuition about how
Stata will treat a missing value to come short suprisingly
often, and this is another example of where it doesn't do
what I would think.
I've often wished for a "negative" missing (a la -99)
value, so I could simply:
replace x = -abs(x) if missing(x)
so that in contexts where I would rather treat missing
as the smallest rather than largest value, I could do so
in one stroke instead of trying to trick, eg, -bys y (x)-
into doing what I want.
j
Nick Cox wrote:
I don't use -gsort- much, as I usually prefer to work out my own
-sort- order without wanting to re-discover
the precise idiosyncratic syntax of -gsort-. (I've got a blind spot on
-recode- for the same kind of reason.)
(That's not on a par with B*ll G???d, who can write the equivalent of
an -egen- function several times faster than it takes to find out
whether that function already exists.)
But -- to the point -- while what Brian says is a fair answer it seems
to me to point to a missing option on -gsort-.
-reallydowantmissingfirst- would not be very Stataish as a name, but
Fred Wolfe's want and need seemed very reasonable to me.
Nick [email protected]
Brian P. Poi
On Thu Jul 5 06:58:30 2007, Fred Wolfe wrote:
Is there a problem with gsort (Stata 10 and below) or am I
misunderstanding something?
I have a variable called -phdif-. I want the greatest value of that
variable to appear in the last observation. There are
missing values,
so I use -gsort- with the -mfirst- option.
...
. gsort phdif
. l phdif in 1,clean
phdif
1. 1
. l phdif in l,clean
phdif
169914. .
The problem appears to be that missings are still last even
though I
used the -mfirst- option.
Any suggestions? Is this a problem or am I thinking about this
incorrectly?
The "mfirst" option of -gsort- applies only to variables sorted in
descending order.
Stata stores missing values as extremely large numbers, so if a
variable is sorted in descending order, missing values should appear
first in the list since they are greater than all non-missing values.
-gsort-, however, tries to be helpful when sorting in descending
order by putting the missing values at the end of the list, assuming
that the user really cares about the large real values of the
variable, not the missing values.
The "mfirst" option tells -gsort- to put the missing values first in
the list instead of trying to be helpful by putting them at the end
of the list.
If you want to get the missing values to appear first when doing an
ascending sort, one way to proceed is to create a 0/1 variable equal
to 0 if the variable of interest contains missing and 1 otherwise and
then sort by the indicator variable and the variable of interest:
. sysuse auto
. generate missrep78 = cond(missing(rep78), 0, 1)
. gsort missrep78 rep78
. list rep78 in 1/7, sep(0)
+-------+
| rep78 |
|-------|
1. | . |
2. | . |
3. | . |
4. | . |
5. | . |
6. | 1 |
7. | 1 |
+-------+
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