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Re: st: RE: extracting a specific portion of a string
From
Nick Cox <[email protected]>
To
[email protected]
Subject
Re: st: RE: extracting a specific portion of a string
Date
Thu, 17 Mar 2011 09:04:54 +0000
I agree with Eric and Travis. You need to look at the string
functions. This repeats Eric's main suggestions, but I am going to
spell out the underlying principles a bit more.
Much of the most valuable trickery was also exhibited in the very
recent thread started by Rebecca Pope.
First, as a small matter of personal taste, I am going to work in
lower case. Too much SHOUTING otherwise. It should be easy to
translate my code to the upper case version.
So, I presume a prior
gen lc = lower(v1)
For similar problems I always consider trying -strpos()- first.
-strpos()- returns the position of a substring and is non-zero when it
occurs and zero otherwise. If the feeling is that exact position of
substring is immaterial, then the twist that
strpos(strvar, "interesting substring") > 0
is 1 whenever "interesting substring" occurs and 0 otherwise gives
this function spin for this problem. Note the good taste of StataCorp
in not including a function -includes()- or -contains()- returning
true or false; such a function is superfluous, redundant and otiose
once you know this trick.
I would proceed step-by-step and generate indicators
gen is_blood = strpos(lc, "blood") > 0
gen is_serum = strpos(lc, "serum") > 0
and then classify e.g.
gen what_have_we got = cond(is_blood & !is_serum, 1,
cond(is_serum & !is_blood, 2,
cond(is_serum & is_blood, 3, 4)))
What could go wrong? Spelling mistakes for one. What happens if it is
"blod" or "bloood", and so forth? That's why there is a ragbag
category in the variable just created that you should look at.
Sometimes you can fix a few spelling mistakes quickly.
Sometimes you need the more powerful machinery of -regexm()- and -regexs()-.
On a detail that might confuse: Eric used -index()- and -strpos()-. In
essence, -index()- is the old name that still works, while -strpos()-
is the new name. It's the same function underneath the names.
Nick
On Thu, Mar 17, 2011 at 4:15 AM, Eric Booth <[email protected]> wrote:
> On Mar 16, 2011, at 10:43 PM, Travis Coan wrote:
>>
>> I would take a look at the -substr- function -- typing 'help substr' should get you there.
>>
>
> You should probably look at all the functions available in -help string_functions-.
> Note that -substr- alone wouldn't return the desired result in this example, e.g.:
>
> **********************!
> clear
> inp str20(v1)
> "BLOOD"
> "BLOOD(LIPEMIC)"
> "BLOOD(MODERATELYLY"
> "BLOOD, 2ND SPECIMEN"
> "BLOOD,1STSPECIMEN"
> "BLOOD,2NDSPECIMEN"
> "MOTHER'SBLOOD"
> "SERUM,1STSPECIMEN"
> "SERUM,2NDSPECIMEN"
> end
>
> g v2 = substr(v1, 1, 5)
> **note obs 7
>
> //using strpos and substr string functions//
> g str10 v4 = ""
> foreach x in "BLOOD" "SERUM" {
> g v`x' = strpos(v1, "`x'")
> replace v4 = substr(v1, v`x' , 5) if v`x'>0
> }
>
> //using index//
> g ind = 0
> replace ind = 1 if index(v1, "BLOOD")
> replace ind = 2 if index(v1, "SERUM")
> la def ii 1 "Blood" 2 "Serum", modify
> lab val ind ii
> li
> **********************!
Mendoza Aldana, Dr Jorge Antonio (WPRO)
>> My dataset has a string variable, from which I need a specific portion of it. The content of the variable is like:
>>
>> BLOOD
>> BLOOD(LIPEMIC)
>> BLOOD(MODERATELYLY
>> BLOOD, 2ND SPECIMEN
>> BLOOD,1STSPECIMEN
>> BLOOD,2NDSPECIMEN
>> MOTHER'SBLOOD
>> SERUM,1STSPECIMEN
>> SERUM,2NDSPECIMEN
>>
>> and I need to generate a new variable containing either "BLOOD" or "SERUM"
>> I would appreciate very much if you can give me some hints on solving this.
>> I'm using Stata 11.1 on a Windows XP machine
I agree with Eric and Travis. You need to look at the string
functions. This repeats
Much of the most valuable trickery was exhibited in the very recent
thread started by Rebecca Pope.
First, as a small matter of personal taste, I am going to work in
lower case. Too much SHOUTING otherwise. It should be easy to
translate my code to the upper case version.
So, I presume a prior
gen lc = lower(v1)
I would try using -strpos()- first. -strpos()- returns the position of
a substring and is non-zero when it occurs and zero otherwise. If the
feeling is that exact position of substring is immaterial, then the
twist that
strpos(strvar, "interesting substring") > 0
is 1 whenever "interesting substring" occurs and 0 otherwise gives
this function spin for this problem. Note the good taste of StataCorp
in not including a function -includes()- or -contains()- returning
true or false; such a function is superfluous, redundant and otiose
once you know this trick.
I would proceed step-by-step and generate indicators
gen is_blood = strpos(lc, "blood") > 0
gen is_serum = strpos(lc, "serum") > 0
and then classify e.g.
gen what_have_we got = cond(is_blood & !is_serum, 1,
cond(is_serum & !is_blood, 2,
cond(is_serum & is_blood, 3, 4)))
What could go wrong? Spelling mistakes for one. What happens if it is
"blod" or "bloood", and so forth? That's why there is a ragbag
category in the variable just created that you should look at.
Sometimes you can fix a few spelling mistakes quickly.
Sometimes you need the more powerful machinery of -regexm()- and -regexs()-.
Nick
On Thu, Mar 17, 2011 at 4:15 AM, Eric Booth <[email protected]> wrote:
> On Mar 16, 2011, at 10:43 PM, Travis Coan wrote:
>>
>> I would take a look at the -substr- function -- typing 'help substr' should get you there.
>>
>
> You should probably look at all the functions available in -help string_functions-.
> Note that -substr- alone wouldn't return the desired result in this example, e.g.:
>
> **********************!
> clear
> inp str20(v1)
> "BLOOD"
> "BLOOD(LIPEMIC)"
> "BLOOD(MODERATELYLY"
> "BLOOD, 2ND SPECIMEN"
> "BLOOD,1STSPECIMEN"
> "BLOOD,2NDSPECIMEN"
> "MOTHER'SBLOOD"
> "SERUM,1STSPECIMEN"
> "SERUM,2NDSPECIMEN"
> end
>
> g v2 = substr(v1, 1, 5)
> **note obs 7
>
> //using strpos and substr string functions//
> g str10 v4 = ""
> foreach x in "BLOOD" "SERUM" {
> g v`x' = strpos(v1, "`x'")
> replace v4 = substr(v1, v`x' , 5) if v`x'>0
> }
>
> //using index//
> g ind = 0
> replace ind = 1 if index(v1, "BLOOD")
> replace ind = 2 if index(v1, "SERUM")
> la def ii 1 "Blood" 2 "Serum", modify
> lab val ind ii
> li
> **********************!
Mendoza Aldana, Dr Jorge Antonio (WPRO)
>> My dataset has a string variable, from which I need a specific portion of it. The content of the variable is like:
>>
>> BLOOD
>> BLOOD(LIPEMIC)
>> BLOOD(MODERATELYLY
>> BLOOD, 2ND SPECIMEN
>> BLOOD,1STSPECIMEN
>> BLOOD,2NDSPECIMEN
>> MOTHER'SBLOOD
>> SERUM,1STSPECIMEN
>> SERUM,2NDSPECIMEN
>>
>> and I need to generate a new variable containing either "BLOOD" or "SERUM"
>> I would appreciate very much if you can give me some hints on solving this.
>> I'm using Stata 11.1 on a Windows XP machine
>> Kind regards,
>> Jorge
>>
>>
>>
>>
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