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# st: RE: Cut function

 From "Nick Cox" To Subject st: RE: Cut function Date Wed, 28 Jul 2010 17:04:38 +0100

```You can have anything you like with zero observations: it just won't be visible in your dataset.

More seriously:

I don't understand your precise problem but I've never wanted to use -egen, cut()- (as compared with -egen, group()- which I use very frequently).

If I want to coarsen, I always want to use constant intervals and to be totally clear which way things were rounded. I thus turn to -floor()- or -ceiling()-. Of course, other people often want otherwise.

To give a non-time series example:

. sysuse auto
(1978 Automobile Data)

. clonevar mpg2 = mpg

. replace mpg2 = 5 * floor(mpg/5)
(60 real changes made)

. tab mpg2

Mileage |
(mpg) |      Freq.     Percent        Cum.
------------+-----------------------------------
10 |          8       10.81       10.81
15 |         27       36.49       47.30
20 |         20       27.03       74.32
25 |         12       16.22       90.54
30 |          4        5.41       95.95
35 |          2        2.70       98.65
40 |          1        1.35      100.00
------------+-----------------------------------
Total |         74      100.00

Thus with -floor()- you can round down; your definition will be transparent once you know what -floor()- does; and the resulting values will be automatically self-explanatory. Rounding up just requires -ceil()- instead.

There is more at

SJ-3-4  dm0002  . . . . . . . . Stata tip 2: Building with floors and ceilings
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
Q4/03   SJ 3(4):446--447                                 (no commands)
tips for using floor() and ceil()

Some years ago I suggested to StataCorp that -floor()- and -ceil()- be extended to allow two arguments so that -floor(mpg, 5)- would have the effect above, but while I am still waiting it's easy enough to apply rounding to any interval.

Nick
n.j.cox@durham.ac.uk

Katia Bobulova

I used the command egen cut to divide the time in 5-min intervals.

My 5-min intervals start from 9:30, however, for some days the time
starts for example at 9:40 and so on.

Is there a way to have the time interval with zero observations?

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