Yesterday, Sylvain Friederich posted a problem
on Statalist. As a result of musing on that, I have updated the
-modes- and -extremes- packages, which, thanks
to Kit Baum, are now available in revised form on SSC. Both
packages require Stata 8. -extremes- was born under
Stata 8. A Stata 6 version of -modes- is
still accessible from STB files (-search modes-).
-extremes- by default did, and does, this:
. extremes mpg
+------------+
| obs: mpg |
|------------|
| 26. 12 |
| 27. 12 |
| 11. 14 |
| 12. 14 |
| 28. 14 |
+------------+
+------------+
| 68. 31 |
| 43. 34 |
| 57. 35 |
| 66. 35 |
| 71. 41 |
+------------+
note: 6 values of 14
Now there is a new -frequencies- option which
shows not the # extreme values, but the #
extreme classes, in both tails (one tail
only is optional):
. extremes mpg, frequencies
+-------------+
| freq: mpg |
|-------------|
| 2 12 |
| 6 14 |
| 2 15 |
| 4 16 |
| 4 17 |
+-------------+
+-------------+
| 2 30 |
| 1 31 |
| 1 34 |
| 2 35 |
| 1 41 |
+-------------+
In other words, think of a variable treated
discretely: you see the frequencies of the
leftmost and rightmost bars of the
corresponding discrete histogram.
The -modes- program gives the -modes- package
its name. -modes- now has a new option to
specify the number of modes:
. modes mpg, nmodes(5)
----------------------
Mileage |
(mpg) | Freq.
----------+-----------
14 | 6
18 | 9
19 | 8
21 | 5
22 | 5
25 | 5
----------------------
Note that here 5 is treated as
a request, not an instruction,
given the possibility of ties.
The -modes- package also
includes a new -rare- command,
which by default shows singletons:
. rare mpg
----------------------
Mileage |
(mpg) | Freq.
----------+-----------
29 | 1
31 | 1
34 | 1
41 | 1
----------------------
The need for -rare- is perhaps
rare; nevertheless this was part of
Sylvain's problem and others may find
it useful. In British, and perhaps
in other forms of English, we talk
of searching for a needle in a haystack,
and, if you face a variant on that, -rare-
may come in handy.
Nick
[email protected]
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