How to create a prop.table() for a three dimension table?

r

Solution

You can specify multiple levels of input to the `prop.table` function, where 1=row, 2=column, 3=strata etc etc

Simple example:

test <- 1:8
dim(test) <- c(2,2,2)
test
, , 1

     [,1] [,2]
[1,]    1    3
[2,]    2    4

, , 2

     [,1] [,2]
[1,]    5    7
[2,]    6    8

Then you can do things like:

# % of all values in each stratum/sub-table
prop.table(test,3)

# row % within each stratum/sub-table
prop.table(test,c(3,1))

# column % within each stratum/sub-table
prop.table(test,c(3,2))

There might be a simple way to deal with `NA`s, but a roundabout version would be to set them as `0`'s and then reset as `NA`'s:

# set one of the values to NA as an example
test[7] <- NA

# do the procedure
nas <- is.na(test)
test[nas] <- 0
result <- prop.table(test,c(3,2))
result[nas] <- NA

result
, , 1

          [,1]      [,2]
[1,] 0.3333333 0.4285714
[2,] 0.6666667 0.5714286

, , 2

          [,1] [,2]
[1,] 0.4545455   NA
[2,] 0.5454545    1

Problem

Could you let know how I can get percentages in a `three dimensional` table. I know how to create percentages in a `two dimensional` table by runnin the following ``` p <-with(mtcars,tapply(carb,list(cyl,vs),length)) prop.table(p,2) # by column ``` However, if I can try to add another variable, I dont how to do? ``` p <- with(mtcars,tapply(carb,list(cyl,vs,gear),length)) ```

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