RE: st: Extracting substrings from variable and combining variables.

[Nick Cox <n.j.cox@durham.ac.uk>]

-egen, concat()- "didn't work": this can not be discussed without reference to exactly (a) what you want to do, (b) what you tried and (c) what happened. 

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

Amal Khanolkar

Hi Nick & Brendan,

Thanks so much for your help with the 'regex' commands in retrieving subjects with a common diagnosis from my dataset.

I know have 12 such 'diagnostic' variables (preght1-12) all for say hypertension ( 12, as a patient might have received this diagnosis as the 1st or 7th or 12th diagnosis when admitted to hospital).

I need to combine these 12 variables into one. I tried doing this using the 'egen' command with the concat function but it didn't work. Any tips on other commands I could try?

The variables look like this and most of the 12 variables have the same 3 categories, but some have just 2 or 1:

                         tab preght1

    preght1 |      Freq.     Percent        Cum.
------------+-----------------------------------
        637 |      8,314       20.76       20.76
        642 |     21,268       53.11       73.88
         O1 |     10,461       26.12      100.00
------------+-----------------------------------
      Total |     40,043      100.00


.                         tab preght2

    preght2 |      Freq.     Percent        Cum.
------------+-----------------------------------
        637 |     11,202       33.51       33.51
        642 |     15,191       45.44       78.95
         O1 |      7,036       21.05      100.00
------------+-----------------------------------
      Total |     33,429      100.00



.                         tab preght4

    preght4 |      Freq.     Percent        Cum.
------------+-----------------------------------
        637 |        797       18.02       18.02
        642 |      1,747       39.51       57.53
         O1 |      1,878       42.47      100.00
------------+-----------------------------------
      Total |      4,422      100.00



. des  preght1

              storage  display     value
variable name   type   format      label      variable label
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
preght1         str3   %9s                    



Thanks,

/Amal.

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] on behalf of Nick Cox [njcoxstata@gmail.com]
Sent: 25 May 2012 20:22
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Extracting substrings from variables.

As any leading spaces surely don't matter, consider using

regexm(ltrim(mdiag1x), "^(637|642|O1)")

Nick

On Fri, May 25, 2012 at 7:17 PM, Brendan Halpin <brendan.halpin@ul.ie> wrote:
> On Fri, May 25 2012, Nick Cox wrote:
>
>> . di regexm("Stata rules OK O1", "^637|642|O1")
>> 1
>
> OK, I was wrong that the grouping parentheses were unnecessary. However,
> the way I used them first was also wrong.
>
> Something like this is needed:
>
> . gen pright = regexs(0) if regexm(mdiag1x, "^(637|642|O1)")
>
> More evidence that Nick's reluctance about regexp is not unwise.
>

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