R coding: How to keep records with 4 complete quarters of data

Question

I have a dataframe with company quarterly data and have this question:

How can I retain records for only those companies with 4 quarters of data (as companies sometimes

Answer 1

Here is the code that can help you:

library(data.table)
data<-data.table( year, qtr, company, IQ, REVQ, AssetQ, CashQ)
fullyr <- data[,.(len=.N),by=.(year)][len == 4]
data <- data[year %in% fullyr$year]

Requesting you to provide the code you have tried for solution next time :)