[R] abs(U) > 0 where U is a vector?

[Alberto Monteiro]

Benjamin Dickgiesser wrote:
> 
> I am looking for a way to compare if every element of a vector is > 0.
> 
> i.e.
> while(abs(U) > 0)
> {
> 
> ..
> }
> 
Notice that abs(U) [and, in general, most functions that are
defined on scalars, like sin, cos, exp, ...], when U is a vector,
operates on the _elements_ of U, so abs(U) is just a vector
of non-negative elements.

Likewise, (U > 0) [and, in general, most relations that are
defined on scalars, like (U != 0), (U == 0), (U >= 1 & U <= 2)],
when U is a vector, operates on the _elements_ of U, so (U > 0)
is just a vector of logical values.

So, you must take some operation that will check if all components
of a vector of logical (boolean) elements are non-zero. The most
obvious solution is to _multiply_ those logical elements, because
FALSE will become zero, and zero * anything = zero, so if any
component of U is <= 0, you get zero:

prod(U > 0)

But this is not the most "elegant" solution, because there is
a function to check if all [and another to check if any] component
of a vector of booleans are [is] true: it's all(V) [resp. any(V)].

So:

all(U > 0)

Sanity check:

U <- c(-1, 1, 2)
all(U > 0)  # FALSE
U[1] <- 3
all(U > 0)  # TRUE

Alberto Monteiro