# [R] vector comparison

Karin Lagesen karinlag at studmed.uio.no
Thu Jun 5 12:38:14 CEST 2008

I know this is fairly basic, but I must have somehow missed it in the
manuals.

I have two vectors, often of unequal length. I would like to compare
them for identity. Order of elements do not matter, but they should
contain the same.

I.e: I want this kind of comparison:

> if (1==1) show("yes") else show("blah")
[1] "yes"
> if (1==2) show("yes") else show("blah")
[1] "blah"
>

Only replace the numbers with for instance the vectors

> a = c("a")
> b = c("b","c")
> c = c("c","b")

Now, I realize I only get a warning when comparing things, but this to
me means that I am not doing it correctly:

> if (a==a) show("yes") else show("blah")
[1] "yes"
> if (a==b) show("yes") else show("blah")
[1] "blah"
Warning message:
In if (a == b) show("yes") else show("blah") :
the condition has length > 1 and only the first element will be used
>
> if (b == c) show("yes") else show("blah")
[1] "blah"
Warning message:
In if (b == c) show("yes") else show("blah") :
the condition has length > 1 and only the first element will be used
>

I have also tried the %in% comparator, but that one throws warnings too:

> if (b %in% c) show("yes") else show("blah")
[1] "yes"
Warning message:
In if (b %in% c) show("yes") else show("blah") :
the condition has length > 1 and only the first element will be used
>
> if (c %in% c) show("yes") else show("blah")
[1] "yes"
Warning message:
In if (c %in% c) show("yes") else show("blah") :
the condition has length > 1 and only the first element will be used
>

So, how is this really supposed to be done?

Thanks!

Karin

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