To check if a hash (also known as a dictionary or associative array) includes a key in R, the %in% operator can be used. Here is an example:
# create a hash
my_hash <- list(a = 1, b = 2, c = 3)
# check if a key exists
"a" %in% names(my_hash) # returns TRUE
# check if a key does not exist
"d" %in% names(my_hash) # returns FALSE
In this example, the my_hash hash is created with three key-value pairs. The %in% operator is then used to check if the hash includes the key "a". The expression names(my_hash) returns a character vector of the keys in the hash, and %in% checks if the string "a" is included in that vector. The result is a logical value of TRUE. Similarly, the %in% operator can be used to check for non-existence of a key by checking if a key is not included in the vector of keys, such as in the case of checking for the key "d".