[R] Detect and replace omitted data

[David Winsemius]

On Oct 18, 2011, at 2:24 PM, Sarah Goslee wrote:

> Hi Jonny,
>
> On Tue, Oct 18, 2011 at 1:02 PM, Jonny Armstrong
> <jonny5armstrong at gmail.com> wrote:
>> I am analyzing the spatial distribution of fish in a stream. The  
>> stream is
>> divided into equally sized units, and the number of fish in each  
>> unit is
>> counted. My problem is that my dataset is missing rows where the  
>> count in a
>> unit equals zero. I need to create zero data for the missing units.
>>
>> For example:
>> day<-(c(rep(4,8),rep(6,8)))
>> unit<-c(seq(1,8,1),seq(2,16,2))
>> value<-floor(rnorm(16,25,10))
>> x<-cbind(day,unit,value)
>
> Thanks for the actual reproducible example.
>
>> x
>>      day unit value
>>  [1,]   4    1    19
>>  [2,]   4    2    15
>>  [3,]   4    3    16
>>  [4,]   4    4    20
>>  [5,]   4    5    17
>>  [6,]   4    6    15
>>  [7,]   4    7    14
>>  [8,]   4    8    29
>>  [9,]   6    2    18
>> [10,]   6    4    22
>> [11,]   6    6    27
>> [12,]   6    8    16
>> [13,]   6   10    45
>> [14,]   6   12    36
>> [15,]   6   14    34
>> [16,]   6   16    13
>>
>> Lets say the stream has 16 units. For each day, I want to fill in  
>> rows for
>> any missing units (e.g., units 9-16 for day 4, the odd numbered  
>> units on day
>> 6) with values of zero.

I could not figure out what you wanted precisely. If "day" is the row  
designator, and you want values by 'unit' and 'day' with zeros for the  
missing, then that is exactly what `xtab` delivers:

 > xtabs(value ~ day+unit, data=x)
    unit
day  1  2  3  4  5  6  7  8 10 12 14 16
   4 25 34  3 25 38 18 19 33  0  0  0  0
   6  0 22  0 42  0 37  0  4 12 31 17 28

You cannot get much more concise than that.

-- 
david.
>
> Here's one option, though it may not be terribly concise:
>
> all.samples <- expand.grid(day=unique(x[,"day"]), unit=1:16)
> all.samples <- all.samples[order(all.samples[,"day"],  
> all.samples[,"unit"]),]
> x.final <- merge(x, all.samples, all.y=TRUE)
> x.final[is.na(x.final[,"value"]), "value"] <- 0
>
> Sarah
>
>> Does anyone know a relatively concise way to do this?
>> Thank you.
>>
>>        [[alternative HTML version deleted]]
>>
>
> -- 
> Sarah Goslee
> http://www.functionaldiversity.org
>
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> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT