Finding change in values

Shell Programming and Scripting
1

I have an array

X = ( -100 -90 -80 -70 -60 -50 -40 30 40 50 60 70 80 90 100 )

I want to find the place where values change from negative to positive.

2

Which programming language are you using?

3

awk should be ok

4 
echo '-100 -90 -80 -70 -60 -50 -40 30 40 50 60 70 80 90 100' | nawk '{for(i=1;i++<NF;) if($i*$(i+1)<0) {print i+1;next}}'
5

In case multiple changes should be handled:

awk 'BEGIN {
  n = split("-100 -90 -80 -70 -60 -50 -40 30 40 50 60 70 80 90 100", x)
  for (i = 0; ++i <= n;) {
    if (i > 1) 
      (x > 0) == l || r = r ? r FS i : i
    l = x > 0 
    }
  print "+/- changes in position(s):", r    
  }'

For example:

% awk 'BEGIN {
  n = split("100 -90 -80 -70 -60 -50 -40 30 40 -50 60 70 80 90 100", x)
  for (i = 0; ++i <= n;) {
     if (i > 1) 
      (x > 0) == l || r = r ? r FS i : i
    l = x > 0
   }
  print "+/- changes in position(s):", r
  }'
+/- changes in position(s): 2 8 10 11
6

yep, good idea:

echo '-100 -90 -80 4 5 6 -70 -60 -50 -40 30 40 50 60 70 80 90 100' | nawk '{l="";for(i=1;i++<NF;) if($i*$(i+1)<0) {l=l FS i+1} print "+/- changes in position(s):" l}'
7

Does this code work if the first element is 100 and not -100?

8

good catch - thanks!

echo '100 -90 -80 4 5 6 -70 -60 -50 -40 30 40 50 60 70 80 90 100' | nawk '{l="";for(i=1;i<=NF;i++) if($i*$(i+1)<0) {l=l FS i+1} print "+/- changes in position(s):" l}'
9

Forgot to mention that values are always ascending. So don't need it so great.