How to avoid NA columns in dcast() output?

Question

How can I avoid NA columns in dcast() output from the reshape2 package?

In this dummy example the dcast() o

Answer 1

library(dplyr)
library(tidyr)
iris %>%
  filter(!is.na(Species2)) %>%
  group_by(Species, Species2) %>%
  summarize(freq = n()) %>%
  spread(Species2, freq)