问题
I am wondering how to create a subset of data in R based on a list of dates, rather than by a date range.
For example, I have the following data set data which contains 3 years of 6-minute data.
date zone month day year hour minute temp speed gust dir
1 09/06/2009 00:00 PDT 9 6 2009 0 0 62 2 15 156
2 09/06/2009 00:06 PDT 9 6 2009 0 6 62 13 16 157
I have used breeze<-subset(data, ws>=15 & wd>=247.5 & wd<=315, select=date:dir) to select the rows which meet my criteria for a sea breeze, which is fine, but what I want to do is create a subset of the days which contain those times that meet my criteria.
I have used...
as.character(breeze$date)
trimdate<-strtrim(breeze$date, 10)
breezedate<-as.Date(trimdate, "%m/%d/%Y")
breezedate<-format(breezedate, format="%m/%d/%Y")
...to extract the dates from each row that meets my criteria so I have a variable called breezedate that contains a list of the dates that I want (not the most eloquent coding to do this, I'm sure). There are about two-hundred dates in the list. What I am trying to do with the next command is in my original dataset data to create a subset which contains only those days which meet the seabreeze criteria, not just the specific times.
breezedays<-(data$date==breezedate)
I think one of my issues here is that I am comparing one value to a list of values, but I am not sure how to make it work.
回答1:
Lets assume your breezedate list looks like this and data$date is simple string:
breezedate <- as.Date(c("2009-09-06", "2009-10-01"))
This is probably want you want:
breezedays <- data[as.Date(data$date, '%m/%d/%Y') %in% breezedate]
回答2:
The intersect() function (docs) will allow you to compare one data frame to another and return those records that are the same.
To use, run the following:
breezedays <- intersect(data$date,breezedate) # returns into breezedays all records that are shared between data$date and breezedate
来源：https://stackoverflow.com/questions/18725014/selecting-specific-dates-in-r