On Fri, 13 Sep 2013, William Dunlap wrote:
findInterval(thresholds, values)
[1] 1 4 4 4 7
Thanks a lot! But now I have a new problem, a typical R issue perhaps.
First, let's look at a successful case:
> thresholds <- c(1,3,5,7,9)
> values <- c(0.854, 1.648, 1.829, 1.874, 7.670, 7.673, 7.722)
> values[findInterval(thresholds, values)]
[1] 0.854 1.874 1.874 1.874 7.722
Then a new batch of values came, notice only the first element of new values
differ:
> thresholds <- c(1,3,5,7,9)
> values <- c(1.254, 1.648, 1.829, 1.874, 7.670, 7.673, 7.722)
> findInterval(thresholds, values)
[1] 0 4 4 4 7
> values[findInterval(thresholds, values)]
[1] 1.874 1.874 1.874 7.722
This is a surprise. The desirable output is:
[1] 0 1.874 1.874 1.874 7.722
This is desirable, because so maintains the same number of elements during
calculation. (You may suggest leaving out the indices and try to calculate
maximum-values-below-threshold directly, but the indices are useful to
address other fields in the data frame whence values came.)
This problem can be simplified as following:
in R, we have:
> a <- 1:10
> a[c(1,3)]
[1] 1 3
> a[c(0,3)]
[1] 3
While I was hoping to get:
> a <- 1:10
> a[c(1,3)]
[1] 1 3
> a[c(0,3)]
[1] 0 3
The straightforward solution, is to shift the whole test values one
position, so that the first value is always zero:
> values <- c(0, 1.254, 1.648, 1.829, 1.874, 7.670, 7.673, 7.722)
This solution, despite begetting a train of changes elsewhere in the code,
is semantically wrong, since the first element of values should be the first
value, now it is actually the 0-th value.
What would you do in the case?
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