check whether a variable is in increasing order in R

Question

Supposing I have a variable

x <- c(1,3,5,7,8)

Now x is in increasing order

How to check whether a variable is in increasing order in R?

Answer 1

From ?is.unsorted:

Test if an object is not sorted (in increasing order) ...

So, in this case, you could:

is.sorted = Negate(is.unsorted)
is.sorted(x)
#[1] TRUE
#> is.sorted(1:5)
#[1] TRUE
#> is.sorted(5:1)
#[1] FALSE
#> is.sorted(sample(5))
#[1] FALSE
#> is.sorted(sort(runif(5)))
#[1] TRUE
#> is.sorted(c(1,2,2,3))
#[1] TRUE
#> is.sorted(c(1,2,2,3), strictly = T)
#[1] FALSE

This function is fast, because it loops over the vector and breaks the loop as soon as an element is not ">=" (or ">", if "strictly = T") from the previous one.

Answer 2

Try this:

all(diff(x) > 0)

or

all(diff(x) >= 0)

I agree with @flodel that is.unsorted (h/t @alexis_laz) is probably even better.

Answer 3

Look at the differences:

R> x <- c(1,3,5,7,8) 
R> allIncreasing <- function(x) all(diff(x)>0)
R> allIncreasing(x)
[1] TRUE
R> y <- x; y[3] <-0 
R> allIncreasing(y)
[1] FALSE
R>