[R] about interpolating data in r

Jim Lemon
Fri, 22 Jul 2016 10:07:37 -0000

Hi lili,
The problem may lie in the fact that I think you are using
"interpolate" when you mean "extrapolate". In that case, the
best you
can do is spread values beyond the points that you have. Find the
slope of the line, put a point at each end of your time data
(2009-01-01 and 2009-12-31) and use "approx" on all three gaps. Note
that this slope is a slippery one indeed and few will accept that the
values so generated mean anything.

Jim

On Fri, Jul 22, 2016 at 9:38 AM, Ismail SEZEN <sezenismail at gmail.com>
wrote:
>
>> On 22 Jul 2016, at 01:54, lily li <chocold12 at gmail.com> wrote:
>>
>> Thanks, I meant if there are missing data at the beginning and end of a
>> dataframe, how to interpolate according to available data?
>>
>> For example, the A column has missing values at the beginning and end,
how
>> to interpolate linearly between 10 and 12 for the missing values?
>>
>> df <- data.frame(A=c(NA, NA,10,11,12,
NA),B=c(5,5,4,3,4,5),C=c(3.3,4,3,1.5,
>> 2.2,4),time=as.Date(c("1990-01-01","1990-02-
>>
07","1990-02-14","1990-02-28","1990-03-01","1990-03-20")))
>>
>
> As William was answered;
>
> with(df, approx(x=time, y=A, xout=seq(min(time, na.rm =T), max(time, na.rm
= T), by="days")))
>
> will help you interpolate linearly between knwon values even column has
NA?s.
>
>
>>
>> On Thu, Jul 21, 2016 at 4:48 PM, William Dunlap <wdunlap at
tibco.com> wrote:
>>
>>> Try approx(), as in:
>>>
>>> df <-
>>>
data.frame(A=c(10,11,12),B=c(5,5,4),C=c(3.3,4,3),time=as.Date(c("1990-01-01","1990-02-07","1990-02-14")))
>>> with(df, approx(x=time, y=C, xout=seq(min(time), max(time),
by="days")))
>>>
>>> Do you notice how one can copy and paste that example out of the
>>> mail an into R to see how it works?  It would help if your
questions
>>> had that same property - show how the example data could be
created.
>>>
>>>
>>> Bill Dunlap
>>> TIBCO Software
>>> wdunlap tibco.com
>>>
>>> On Thu, Jul 21, 2016 at 3:34 PM, lily li <chocold12 at
gmail.com> wrote:
>>>
>>>> I have a question about interpolating missing values in a
dataframe. The
>>>> dataframe is in the following, Column C has no data before
2009-01-05 and
>>>> after 2009-12-31, how to interpolate data for the blanks? That
is to say,
>>>> interpolate linearly between these two gaps using 5.4 and 6.1?
Thanks.
>>>>
>>>>
>>>> df
>>>> time                A      B     C
>>>> 2009-01-01    3      4.5
>>>> 2009-01-02    4      5
>>>> 2009-01-03    3.3   6
>>>> 2009-01-04    4.1   7
>>>> 2009-01-05    4.4   6.2   5.4
>>>> ...
>>>>
>>>> 2009-11-20    5.1   5.5   6.1
>>>> 2009-11-21    5.4   4
>>>> ...
>>>> 2009-12-31    4.5   6
>>>>
>>>>        [[alternative HTML version deleted]]
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and
more, see
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible
code.
>>>>
>>>
>>>
>>
>>       [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.