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 <sewa...@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.4...@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 <sewa...@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 <dcarl...@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-boun...@r-project.org] On Behalf Of Ashta
>>>> Sent: Saturday, November 21, 2015 11:53 AM
>>>> To: R help <r-help@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@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@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@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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