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Re: st: drop observations - if statement
From
Nick Cox <[email protected]>
To
"[email protected]" <[email protected]>
Subject
Re: st: drop observations - if statement
Date
Thu, 6 Mar 2014 11:52:56 +0000
Note also that in general Stata is highly literal when dealing with
strings. Indeed it could hardly be anything else.
So, when you see instances of "." that you want to -drop- but you ask
that Stata -drop- instances of "", your command cannot have the
desired effect.
The user-written command -dropmiss- (Stata Journal) has an option
-piasm-, comprehensible as "period is also string missing" for the
convenience of users who wish to regard "." as missing. The existence
of this option is evidence for the general rule, not against it!
Nick
[email protected]
On 6 March 2014 10:35, Nick Cox <[email protected]> wrote:
> "." may seem to mean missing in two possible senses;
>
> 1. Users may employ that coding for missing, but that's a personal
> choice. Stata pays no special attention.
>
> 2. Stata will return numeric missing to -real(".")-
>
> . di real(".")
>
> .
>
> Notice that Stata displayed a period or stop, meaning numeric (often
> called system) missing.
>
> But it does that to anything that can't be translated to a number:
>
> . di real("Stata")
> .
>
> Is "." missing? Stata will answer this question for you
>
> . di missing(".")
> 0
>
> 0 means false.
>
> Nick
> [email protected]
>
>
> On 6 March 2014 03:03, R Zhang <[email protected]> wrote:
>> thank you Jeph!
>>
>> I did "count if missing(cusip)", it shows zero observation. but when
>> the data is openned in browse mode, cusip field is displayed as "." ,
>> is that not missing?
>>
>> On Wed, Mar 5, 2014 at 6:00 PM, Jeph Herrin <[email protected]> wrote:
>>> Are you sure any are missing?
>>>
>>> Try
>>>
>>> count if missing(cusip)
>>>
>>> and see what you get.
>>>
>>> hth,
>>> Jeph
>>>
>>>
>>>
>>>
>>> On 3/5/2014 5:41 PM, R Zhang wrote:
>>>>
>>>> Hi all,
>>>>
>>>> I used the following commands to drop observations based on a string
>>>> variable - CUSIP- that takes missing values, i.e. delete observations
>>>> with missing CUSIP,
>>>>
>>>> drop if cusip==""
>>>>
>>>> cusip is str10
>>>>
>>>> (0 observations deleted)
>>>>
>>>> could you explain why "(0 observations deleted)"?
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