[R] Subsetting by a logical condition and NA's

[Don MacQueen]

>  x <- c(5, NA, 7, 5, NA, 3)
>  y <- c(1,  2, 3, 4,  5, 6)
>  y[x %in% 5]
[1] 1 4

I learned about this trick, if I remember correctly, from reading the 
notes on what's new in the upcoming R 1.5.1

-Don

At 6:17 PM -0700 4/22/02, John Miyamoto wrote:
>I have run into a general problem with subsetting of which the following
>is a simple example.  Suppose that
>
>x <- c(5, NA, 7, 5, NA, 3)
>y <- c(1,  2, 3, 4,  5, 6)
>
>I want to extract the values of y for which x = 5, but y[x==5] yields
>
>>  y[x==5]
>[1]  1 NA  4 NA
>
>I find that y[!is.na(x) & x==5] yields the desired result:
>
>>  y[!is.na(x) & x==5]
>[1] 1 4
>
>but I am wondering whether there is a general way to specify a logical
>condition such that it yields TRUE when the condition is true and FALSE
>when the condition is either false or the input data is NA?  For example,
>is there a simpler way to produce the same results as y[!is.na(x) & x==5]?
>
>John
>
>--------------------------------------------------------------------
>John Miyamoto, Dept. of Psychology, Box 351525
>University of Washington, Seattle, WA 98195-1525
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