Re: st: drop observations - if statement

[R Zhang <r05zhang@gmail.com>]

I need to drop those missing observations for my research goal.

I typed findit dropmiss, and got SJ8-4 dm89_1.  and installed it.

would it be dropmiss(cusip)?

thanks,



On Thu, Mar 6, 2014 at 10:19 AM, Nick Cox <njcoxstata@gmail.com> wrote:
> I can't answer that for you.
>
> It's not necessarily a good idea to -drop- observations just because
> some values are missing. That depends on your research goals, and I
> have no idea what they are. Also, missing values do little harm,
> because Stata usually ignores them.
>
> It's a conditional: if you want to -drop- data with missings,
> -dropmiss- (SJ) is just one tool. But it is, necessarily, no more than
> a wrapper for -drop-, so whatever it does you can do by other means.
>
>
> Nick
> njcoxstata@gmail.com
>
>
> On 6 March 2014 15:11, R Zhang <r05zhang@gmail.com> wrote:
>> 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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