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)

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.

Does anyone know a relatively concise way to do this?
Thank you.

	[[alternative HTML version deleted]]

