Create logical vector of first matching condition-CodePudding

How can one create a logical vector that has TRUE for the first matching condition and FALSE otherwise?

v = rep(1:4, 3)
v == 3
#[1] FALSE FALSE  TRUE FALSE FALSE FALSE  TRUE FALSE FALSE FALSE  TRUE FALSE

== gives TRUE for all values that equals 3, but I want only the first one to be TRUE:

#[1] FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

I came up with potential solutions but it always uses the index and then construct the logical vector, and I was wondering if there were simpler one.

tabulate(match(3, v), nbins = length(v))
#[1] 0 0 1 0 0 0 0 0 0 0 0 0

seq_along(v) == min(which(v == 3))
#[1] FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

CodePudding user response：

We may use

v==3&!duplicated(v)
[1] FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

seq_along(v)==match(3,v)
 [1] FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

CodePudding user response：

In negated vector replaceing which.max of comparison with TRUE.

replace(!v, which.max(v == 3), TRUE)
# [1] FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

Or modulo combined with cumsums.

cumsum(cumsum(v %% 3 == 0)) == 1
# [1] FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE