Nested for loop

I already talk about single for loop in a previous post. The same way we did for loop for a single object, we can do it multiple times.

Here a short example: First import the data from here

library(data.table) #load data.table at least V.1.10 (to have fread function)
data_stand <- fread("data_stand_scale.txt") #read the data

data_stand

     Status      mark Stand_ID.m pattern_state
  1: living        NA          1        state1
  2: living       DBH          1        state2
  3:   dead      dead          1        state1
  4:   dead mortality          1        state1
  5: living        NA          2        state3
 ---                                          
188: living       DBH         38        state2
189:   dead      dead         38        state1
190:   dead mortality         38        state3
191: living        NA         39        state1
192: living       DBH         39        state1

And then we can try a nested loop like this:

result_table <- NULL #create a NULL vector
for (i in unique(data_stand[, Status])) {
    new_data <- data_stand[Status == i]
    summary_all <- NULL #create a NULL vector which will be erase at each loop increment

    for (y in unique(new_data[, mark])) {
        summary <- dim(new_data[mark == y][pattern_state == "state1"])[1]
        summary_all <- cbind(summary_all, summary)
        rownames(summary_all) <- i #to have the rownames according to the Status level
    }
    result_table <- rbind(result_table, summary_all)
}
result_table

And here are the results. I know that we can do it in a simpler way, it was just here as an example and before presenting you the foreach loop which are used to do parallel computing.