Using .SD (II)
You can also apply a single function to every column specified in .SDcols using lapply(). In this exercise, you will calculate the number of unique start stations and zip codes for each month using uniqueN(). uniqueN() returns the number of unique elements in a column/vector/data.table.
Latihan ini adalah bagian dari kursus
Data Manipulation with data.table in R
Petunjuk latihan
Find the total number of unique start stations and zip codes for each month, using start_date to extract the month.
Latihan interaktif praktis
Cobalah latihan ini dengan menyelesaikan kode contoh berikut.
# Find the total number of unique start stations and zip codes per month
unique_station_month <- batrips[, ___(___, ___),
by = ___,
.SDcols = c("start_station", "zip_code")]
unique_station_month