Finding gaps in sequential numbers

Question

I don’t do this stuff for a living so forgive me if it’s a simple question (or more complicated than I think). I‘ve been digging through the archives and found a lot of tips that are close but being a novice I’m not sure how to tweak for my needs or they are way beyond my understanding.

I have some large data files that I can parse out to generate a list of coordinate that are mostly sequential

5 6 7 8 15 16 17 25 26 27 

What I want is a list of the gaps

1-4 9-14 18-24 

I don’t know perl, SQL or anything fancy but thought I might be able to do something that would subtract one number from the next. I could then at least grep the output where the difference was not 1 or -1 and work with that to get the gaps.

Answer 1

With awk :

awk '$1!=p+1{print p+1"-"$1-1}{p=$1}' file.txt 

explanations

• $1 is the first column from current input line
• p is the previous value of the last line
• so ($1!=p+1) is a condition : if $1 is different than previous value +1, then :
• this part is executed : {print p+1 "-" $1-1} : print previous value +1, the - character and fist columns + 1
• {p=$1} is executed for each lines : p is assigned to the current 1st column

Answer 2

interesting question.

sputnick's awk one-liner is nice. I cannot write a simpler one than his. I just add another way using diff:

 seq $(tail -1 file)|diff - file|grep -Po '.*(?=d)' 

the output with your example would be:

1,4 9,14 18,24 

I knew that there is comma in it, instead of -. you could replace the grep with sed to get -, grep cannot change the input text... but the idea is same.

hope it helps.