[R] Conditional Random selection
ruipbarradas at sapo.pt
ruipbarradas at sapo.pt
Sat Nov 21 21:38:11 CET 2015
Hello,
Try
tapply(tab$S1, tab$time, function(x) length(unique(x)))
Hope this helps,
Rui Barradas
Citando Ashta <sewashm at gmail.com>:
> Hi Bert and all,
> I have related question. In each time period there were different
> locations where the samples were collected (S1). I want count the
> number of unique locations (S1) for each unique time period . So in
> time 1 the samples were collected from two locations and time 2 only
> from one location and time 3 from three locations..
>
> tab <- read.table(textConnection(" time S1 rep
> 1 1 1
> 1 2 1
> 1 2 2
> 2 1 1
> 2 1 2
> 2 1 3
> 2 1 4
> 3 1 1
> 3 2 1
> 3 3 1 "),header = TRUE)
>
> what I want is
>
> time S1
> 1 2
> 2 1
> 3 3
>
> Thank you again.
>
> On Sat, Nov 21, 2015 at 1:30 PM, Ashta <sewashm at gmail.com> wrote:
>> Thank you Bert!
>>
>> What I want is at least 500 samples based on random sampling of time
>> period. This allows samples collected at the same time period are
>> included together.
>>
>> Your script is doing what I wanted to do!!
>>
>> Many thanks
>>
>> On Sat, Nov 21, 2015 at 1:15 PM, Bert Gunter <bgunter.4567 at gmail.com> wrote:
>>> David's "solution" is incorrect. It can also fail to give you times
>>> with a total of 500 items to sample from in the time periods.
>>>
>>> It is not entirely clear what you want. The solution below gives you a
>>> random sample of time periods in which X1>0 and the total number of
>>> samples among them is >= 500. It does not give you the fewest number
>>> of periods that can do this. Is this what you want?
>>>
>>> tab[with(tab,{
>>> rownums<- sample(seq_len(nrow(tab))[X1>0])
>>> sz <- cumsum(X2[rownums])
>>> rownums[c(TRUE,sz<500)]
>>> }),]
>>>
>>> Cheers,
>>> Bert
>>>
>>> Bert Gunter
>>>
>>> "Data is not information. Information is not knowledge. And knowledge
>>> is certainly not wisdom."
>>> -- Clifford Stoll
>>>
>>> On Sat, Nov 21, 2015 at 10:56 AM, Ashta <sewashm at gmail.com> wrote:
>>>> Thank you David!
>>>>
>>>> I rerun the your script and it is giving me the first three time periods
>>>> is it doing random sampling?
>>>>
>>>> tab.fan
>>>> time X1 X2
>>>> 2 2 5 230
>>>> 3 3 1 300
>>>> 5 5 2 10
>>>>
>>>> On Sat, Nov 21, 2015 at 12:20 PM, David L Carlson
>>>> <dcarlson at tamu.edu> wrote:
>>>>> Use dput() to send data to the list as it is more compact:
>>>>>> dput(tab)
>>>>>
>>>>> structure(list(time = 1:8, X1 = c(0L, 5L, 1L, 0L, 2L, 3L, 1L,
>>>>> 4L), X2 = c(251L, 230L, 300L, 25L, 10L, 101L, 300L, 185L)),
>>>>> .Names = c("time",
>>>>> "X1", "X2"), class = "data.frame", row.names = c(NA, -8L))
>>>>>
>>>>> You can just remove the lines with X1 = 0 since you don't want
>>>>> to use them.
>>>>>> tab.sub <- tab[tab$X1>0, ]
>>>>>
>>>>> Then the following gives you a sample:
>>>>>> tab.sub[cumsum(sample(tab.sub$X2))<=500, ]
>>>>>
>>>>> Note, that your "solution" of times 6, 7, and 8 will never
>>>>> appear because the sum of the values is 586.
>>>>>
>>>>> David L. Carlson
>>>>> Department of Anthropology
>>>>> Texas A&M University
>>>>>
>>>>> -----Original Message-----
>>>>> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Ashta
>>>>> Sent: Saturday, November 21, 2015 11:53 AM
>>>>> To: R help <r-help at r-project.org>
>>>>> Subject: [R] Conditional Random selection
>>>>>
>>>>> Hi all,
>>>>>
>>>>> I have a data set that contains samples collected over time. In
>>>>> each time period the total number of samples are given (X2) The goal
>>>>> is to select 500 random samples. The selection should be based on
>>>>> time (select time periods until I reach 500 samples). Also the time
>>>>> period should have greater than 0 for X1 variable. X1 is an indicator
>>>>> variable.
>>>>>
>>>>> Select "time" until reaching the sum of X2 is > 500 and if
>>>>> X1 is > 0
>>>>>
>>>>> tab <- read.table(textConnection(" time X1 X2
>>>>> 1 0 251
>>>>> 2 5 230
>>>>> 3 1 300
>>>>> 4 0 25
>>>>> 5 2 10
>>>>> 6 3 101
>>>>> 7 1 300
>>>>> 8 4 185 "),header = TRUE)
>>>>>
>>>>> In the above example, samples from time 1 and 4 will not be selected
>>>>> ( X1 is zero)
>>>>> So I could reach my target by selecting time 6,7, and 8 or time 2 and
>>>>> 3 and so on.
>>>>>
>>>>> Can any one help to do that?
>>>>>
>>>>> ______________________________________________
>>>>> 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.
>
> ______________________________________________
> 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.htmland provide commented,
> minimal, self-contained, reproducible code.
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