if else statement on dataframe obtained by csv in R?

I have uploded two csv files through read.csv

First dataframe as dos_log

Second Csv file as net_pay

I want to do
1) Take new_log_value from dos_log

(let say it is dd-JUN-2017)

2) Then compare it with Trans_month in net_pay(

to see after Jun is value coming is null or not and count number of null)

3) Then stored this result in another dataframe