Convert data frame to matrix without looping - r

Question

The Question:
I have a data frame with a column that shows whether an event occurred, and columns for month, day, and year. These last 3 were converted to a date vector. I want to make a matrix that shows whether or not an event occurred within a given time period. In this matrix, a row represents a site and a column a date. I was able to write a for loop to do it, but it seemed like there might be a better way to do this, either with apply or some other basic operation. How would you do this?
The Code:
#Initialize events matrix
events = matrix(FALSE,nrow(predicted),ncol(predicted))
# Mark the presence of events
for (i in 1:nrow(events)){
if ((days_from_start[i]>-1)&(days_from_start[i]<=ncol(predicted)))
events[i,days_from_start[i]] = !input_data$Event[i]
}
The Background:
The next step is to compare the events matrix against various model outputs with the same shape. There are relatively few events in the data frame compared to the matrix size; the (probably incorrect) assumption is that the data frame completely lists all events and that unlisted matrix cells did not experience an event. I’m very new to R, so I’d be interested in hearing about other approaches to the same problem, if you think I’m going about it the hard way.
The Data:
> input_data$Event[1:5]
[1] FALSE FALSE FALSE FALSE TRUE
> input_data$Year[1:5]
[1] 2010 2010 2011 2010 2010
> days_from_start[1:5]
Time differences in days
[1] 834 1018 1106 847 1055
> dim(predicted)
[1] 649 732

Answer 1

Since events[i,days_from_start[i]] is accessing more or less random locations in the events matrix (since presumably you have no pattern to days_from_start ) , it may be difficult not to use a loop. Possibly something like the following will work. I haven't tested this since you posted no datasets.
foo<- (days_from_start>-1)&(days_from_start<=ncol(predicted) )
index_matrix<-cbind((1:i)[foo],days_from_start[(1:i)[foo]])
events[index_matrix]<-!input_data$Event[index_matrix[,1]]
What the first line does is create a vector of logicals, TRUE where you want to do something
The next line creates a set of index pairs where you're going to insert data into events matrix. The last line does the insertion.