Finding the first occurence of 1-digit number in a list in Raku

Question

I've got a number of lists of various lengths. Each of the lists starts with some numbers which are multiple digits but ends up with a recurring 1-digit number. For instance:

my @d = <751932 512775 64440 59994 9992 3799 423 2 2 2 2>;
my @e = <3750 3177 4536 4545 686 3 3 3>;

I'd like to find the position of the first occurence of the 1-digit number (for @d 7 and for @e 5) without constructing any loop. Ideally a lambda (or any other practical thing) should iterate over the list using a condition such as $_.chars == 1 and as soon as the condition is fulfilled it should stop and return the position. Instead of returing the position, it might as well return the list up until the 1-digit number; changes and improvisations are welcome. How to do it?

Answer 1

You want the :k modifier on first:

say @d.first( *.chars == 1, :k ) # 7
say @e.first( *.chars == 1, :k ) # 5

See first for more information.

To answer your second part of the question:

say @d[^$_] with @d.first( *.chars == 1, :k );
# (751932 512775 64440 59994 9992 3799 423)
say @e[^$_] with @e.first( *.chars == 1, :k );
# (3750 3177 4536 4545 686)

Make sure that you use the with to ensure you only show the slice if first actually found an entry.

See with for more information.