[R] some question about vector[-NULL]
murdoch.duncan at gmail.com
Wed Sep 10 12:45:59 CEST 2014
On 10/09/2014, 3:21 AM, PO SU wrote:
> Dear expeRts,
> I have some programming questions about NULL in R.There are listed as follows:
> 1. I find i can't let a list have a element NULL:
You can do it using
a <- list(ress = 1, res = NULL)
> How can i know i have a named element but it is NULL, not just get a$xxxx,a$iiii,a$oooo there all get NULL
That's a little harder. There are a few ways:
"res" %in% names(a) & is.null(a[["res"]])
identical(a["res"], list(res = NULL))
should all work.
Generally because of the special handling needed, it's a bad idea to try
to store NULL in a list.
> 2.The most important thing:
> b<-NULL or 1
> a<-c(a,b) will work so i don't need to know whether b is null or not,but:
> a[-NULL] can't work!! i just need a[-NULL]==a , how can i reach this purpose?
Using !, and a logical test, e.g.
where nullentry() is a function based on one of the tests above, but
applied to all entries.
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