Handling datefield in indexes?
I have a dataset contai开发者_StackOverflow中文版ning some variable1 and a quarterly datefield. I would like to
table(variable1)
by datefield. Plus I wonder how to use the datefield in an index like
attach(myds)
table(variable1[datefield == "1984-01-01"])
In SQL I would do Something like:
SELECT * FROM myds GROUP BY YEAR(datefield)
but how can I do it in R? I know i could turn it to a character field and strsplit it, but i would prefer to work with real date fields – if possible.
Have look at year
and round_date
in lubridate
.
Partly I can help myself:
format(datefield, "%Y")
helps me to get all the years without string splitting. Still I wonder how the rest (quarterly grouping is possible).
lubridate from Hadley is even better than that, because it returns a numeric object.
Still, my problem to find the best way to find the best way to get frequencies by date. So far I tried:
aggregate(myvar,list(datefield),FUN=table)
and ended up with a list like 1984-04-01 17, 16, 5, 8, 7, 49
This is okay, but still a little bit cumbersome to process. Let's say myvar is some kind of id and I would like to count the appearance of ids over time. Is there an alternative to looping?
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