How to delete groups containing less than 3 rows of data in R? [duplicate]

Answer 1

Throwing the data.table approach here to join the party:

library(data.table)
setDT(my_data)
my_data[ , if (.N >= 3L) .SD, by = .(Year, Site, Brood)]

Answer 2

One way to do it is to use the magic n() function within filter:

library(dplyr)

my_data <- data.frame(Year=1996, Site="A", Brood=c(1,1,2,2,2))

my_data %>% 
  group_by(Year, Site, Brood) %>% 
  filter(n() >= 3)

The n() function gives the number of rows in the current group (or the number of rows total if there is no grouping).

Answer 3

You can also do this using base R:

temp <- read.csv(paste(folder,"test.csv", sep=""), head=TRUE, sep=",")
matches <- aggregate(Parents ~ Year + Site + Brood, temp, FUN="length")
temp <- merge(temp, matches, by=c("Year","Site","Brood"))
temp <- temp[temp$Parents.y >= 3, c(1,2,3,4)]