Summarize Values in R Data Frame

Question

Suppose I have a data frame in R that looks like this...

Time    Event
1       0
1       1
1       0
2       0
2       0
3       0
3       1
3       0
3       1
3       0

On this data frame, I want to get another data frame with a couple summary values. I want the original time, the count of rows with a time equal to or greater than the time in question, and the number of events that occurred at that time.

Example output:

Time    Eligible    Event
1       10          1
2        7          0
3        5          2

I've tried using the match , by , and table functions to accomplish this, but I can't make anything stick. I could do a double for loop... but there's got to be a better way.

How can I do this? I'd like to do it in base R, not using plyr or some other library...

Answer 1

Using only base R , we can loop the unique "Time" using lapply , get the summary statistics based on the conditions described.

 res <- do.call(rbind,lapply(unique(df$Time), function(x) 
          data.frame(Time=x, Eligible=sum(x<=df$Time),
                Event=sum(df$Event[df$Time %in%x]))))

 res
 #  Time Eligible Event
 #1    1       10     1
 #2    2        7     0
 #3    3        5     2

data

 df <- structure(list(Time = c(1L, 1L, 1L, 2L, 2L, 3L, 3L, 3L, 3L, 3L
 ), Event = c(0L, 1L, 0L, 0L, 0L, 0L, 1L, 0L, 1L, 0L)), .Names = c("Time", 
"Event"), class = "data.frame", row.names = c(NA, -10L))

Answer 2

You could use tapply to the same effect

newData <- data.frame(
    Eligible = tapply(myData$Event,myData$Time,length),
    Events = tapply(myData$Event,myData$Time,sum))

If you have multiple summaries, you can lapply over the fields of your data.frame.

Answer 3

Perhaps this is a little bit more interpretable:

countEligible <- function(x, Time) {

  sum(x <= Time)

}

dat1 <- data.frame(Time = unique(dat$Time), Eligible = unique(sapply(dat$Time, function(x) countEligible(x, dat$Time))))

dat2 <- data.frame(Time = unique(dat$Time), Event = tapply(dat$Event, dat$Time, sum))

merge(dat1, dat2)

> merge(dat1, dat2)
  Time Eligible Event
1    1       10     1
2    2        7     0
3    3        5     2