Counting Attempts of an event in R - r

Question

I'm relatively new in R and learning. I have the following data frame = data
ID grade Test_Date
1 56 01-25-2012
1 63 02-21-2016
1 73 02-31-2016
2 41 12-23-2015
2 76 01-07-2016
3 66 02-08-2016
I am looking to count the number of people (in this case only two unique individuals) who passed their tests after multiple attempts(passing is defined as 65 or over). So the final product would return me a list of unique ID's who had multiple counts until their test scores hit 65. This would inform me that approx. 66% of the clients in this data frame require multiple test sessions before getting a passing grade.
Below is my idea or concept more or less, I've framed it as an if statement
If ID appears twice
count how often it appears, until TEST GRADE >= 65
ifelse(duplicated(data$ID), count(ID), NA)
I'm struggling with the second piece where I want to say, count the occurrence of ID until grade >=65.
The other option I see is some sort of loop. Below is my attempt
for (i in data$ID) {
duplicated(datad$ID)
count(data$ID)
Here is where something would say until =65
}
Again the struggle comes in how to tell R to stop counting when grade hits 65.
Appreciate the help!

Answer 1

You can use data.table:
library(data.table)
dt <- fread(" ID grade Test_Date
1 56 01-25-2012
1 63 02-21-2016
1 73 02-31-2016
2 41 12-23-2015
2 76 01-07-2016
3 66 02-08-2016")
# count the number of try per ID then get only the one that have been successful
dt <- dt[, N:=.N, by=ID][grade>=65]
# proportion of successful having tried more than once
length(dt[N>1]$ID)/length(dt$ID)
[1] 0.6666667

Answer 2

Another option, though the other two work just fine:
library(dplyr)
dat2 <- dat %>%
group_by(ID) %>%
summarize(
multiattempts = n() > 1 & any(grade < 65),
maxgrade = max(grade)
)
dat2
# Source: local data frame [3 x 3]
# ID multiattempts maxgrade
# <int> <lgl> <int>
# 1 1 TRUE 73
# 2 2 TRUE 76
# 3 3 FALSE 66
sum(dat2$multiattempts) / nrow(dat2)
# [1] 0.6666667

Answer 3

Here is a method using the aggregate function and subsetting that returns the maximum score for testers that took the the test more than once starting from their second test.
multiTestMax <- aggregate(grade~ID, data=df[duplicated(df$ID),], FUN=max)
multiTestMax
ID grade
1 1 73
2 2 76
To get the number of rows, you can use nrow:
nrow(multiTestMax)
2
or the proportion of all test takers
nrow(multiTestMax) / unique(df$ID)
data
df <- read.table(header=T, text="ID grade Test_Date
1 56 01-25-2012
1 63 02-21-2016
1 73 02-31-2016
2 41 12-23-2015
2 76 01-07-2016
3 66 02-08-2016")