Re: st: drop observations - if statement

[R Zhang <r05zhang@gmail.com>]

Nick,

thanks so much!   I ran di missing("."), it display 0, so . is not missing.

should I still use the user written command you suggested to drop observations?

-Rochelle

On Thu, Mar 6, 2014 at 6:52 AM, Nick Cox <njcoxstata@gmail.com> wrote:
> 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
> njcoxstata@gmail.com
>
>
> On 6 March 2014 10:35, Nick Cox <njcoxstata@gmail.com> 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
>> njcoxstata@gmail.com
>>
>>
>> On 6 March 2014 03:03, R Zhang <r05zhang@gmail.com> 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 <info@flyingbuttress.net> 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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