根据来自另一个数据框的日期条件将一个数据框的n个行子集

Question

I have a dataframe (say Summary) in R:

Begin Date | EndDate | Month | Year | Count
2/1/2014 | 1/31/2015 | Jan | 2014 | 10
3/1/2014 | 2/28/2015 | Feb | 2014 | 10
4/1/2014 | 3/31/2015 | Mar | 2014 | 10
5/1/2014 | 4/30/2015 | Apr | 2014 | 10

Another dataframe (say terms)

Student_Hire_Date | Student_ID
2/1/2014 | 100001
2/2/2014 | 100002
2/3/2014 | 100003
2/4/2014 | 100004
2/5/2014 | 100005

I need an R code that will populate the column "Count", by taking a subset of data from the Terms table where Student_Hire_Date is between 'BeginDate' and 'EndDate' from Summary Table.

An R code equivalent to :

Summary$Count <- "select count(*) from Terms,Summary 
                  where Terms.Student_Hire_Date between
                      Summary.BeginDate and Summary.EndDate"
                  GROUP BY Summary.EndDate

I tried using the following code, but I am getting the same count for every date range.

summary$Count <- nrow(subset(Terms, 
                              !is.na(Student_ID)
                               & Student_Hire_Date >= as.Date(Summary$BeginDate)
                                & Student_Hire_Date <= as.Date(Summary$EndDate)

Please help!!!!!!

Answer 1

Consider sapply to loop through each row to compare Summary row value to Terms row value. Right now you are subsetting the same condition for every row of Summary since the BeginDate and EndDate do not match outside row of assigned new column.

Summary$Count <- sapply(seq_len(nrow(Summary)), function(i) {
       nrow(subset(Terms, !is.na(Student_ID)
                   & Student_Hire_Date >= Summary$BeginDate[[i]]
                   & Student_Hire_Date <= Summary$EndDate[[i]]))
})