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.
Este ejercicio forma parte del curso
Data Manipulation with data.table in R
Instrucciones del ejercicio
Find the total number of unique start stations and zip codes for each month, using start_date to extract the month.
Ejercicio interactivo práctico
Prueba este ejercicio y completa el código de muestra.
# 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