Best way to simulate "group by" from bash

Question

Suppose you have a file that contains IP addresses, one address in each line:

10.0.10.1
10.0.10.1
10.0.10.3
10.0.10.2
10.0.10.1

You need a shell script that counts for each IP address how many times it appears in the file. For the previous input you need the following output:

10.0.10.1 3
10.0.10.2 1
10.0.10.3 1

One way to do this is:

cat ip_addresses |uniq |while read ip
do
    echo -n $ip" "
    grep -c $ip ip_addresses
done

However it is really far from being efficient.

How would you solve this problem more efficiently using bash?

(One thing to add: I know it can be solved from perl or awk, I'm interested in a better solution in bash, not in those languages.)

ADDITIONAL INFO:

Suppose that the source file is 5GB and the machine running the algorithm has 4GB. So sort is not an efficient solution, neither is reading the file more than once.

I liked the hashtable-like solution - anybody can provide improvements to that solution?

ADDITIONAL INFO #2:

Some people asked why would I bother doing it in bash when it is way easier in e.g. perl. The reason is that on the machine I had to do this perl wasn't available for me. It was a custom built linux machine without most of the tools I'm used to. And I think it was an interesting problem.

So please, don't blame the question, just ignore it if you don't like it. :-)

Answer 1

The quick and dirty method is as follows:

cat ip_addresses | sort -n | uniq -c

If you need to use the values in bash you can assign the whole command to a bash variable and then loop through the results.

PS

If the sort command is omitted, you will not get the correct results as uniq only looks at successive identical lines.

Answer 2

sort ip_addresses | uniq -c

This will print the count first, but other than that it should be exactly what you want.

Answer 3

Sort may be omitted if order is not significant

uniq -c <source_file>

or

echo "$list" | uniq -c

if the source list is a variable

Answer 4

It seems that you have to either use a big amount of code to simulate hashes in bash to get linear behavior or stick to the quadratic superlinear versions.

Among those versions, saua's solution is the best (and simplest):

sort -n ip_addresses.txt | uniq -c

I found http://unix.derkeiler.com/Newsgroups/comp.unix.shell/2005-11/0118.html. But it's ugly as hell...

Answer 5

I'd have done it like this:

perl -e 'while (<>) {chop; $h{$_}++;} for $k (keys %h) {print "$k $h{$k}\n";}' ip_addresses

but uniq might work for you.

Answer 6

I understand you are looking for something in Bash, but in case someone else might be looking for something in Python, you might want to consider this:

mySet = set()
for line in open("ip_address_file.txt"):
     line = line.rstrip()
     mySet.add(line)

As values in the set are unique by default and Python is pretty good at this stuff, you might win something here. I haven't tested the code, so it might be bugged, but this might get you there. And if you want to count occurrences, using a dict instead of a set is easy to implement.

Edit: I'm a lousy reader, so I answered wrong. Here's a snippet with a dict that would count occurences.

mydict = {}
for line in open("ip_address_file.txt"):
    line = line.rstrip()
    if line in mydict:
        mydict[line] += 1
    else:
        mydict[line] = 1

The dictionary mydict now holds a list of unique IP's as keys and the amount of times they occurred as their values.

Answer 7

You probably can use the file system itself as a hash table. Pseudo-code as follows:

for every entry in the ip address file; do
  let addr denote the ip address;

  if file "addr" does not exist; then
    create file "addr";
    write a number "0" in the file;
  else 
    read the number from "addr";
    increase the number by 1 and write it back;
  fi
done

In the end, all you need to do is to traverse all the files and print the file names and numbers in them. Alternatively, instead of keeping a count, you could append a space or a newline each time to the file, and in the end just look at the file size in bytes.

Answer 8

The canonical solution is the one mentioned by another respondent:

sort | uniq -c

It is shorter and more concise than what can be written in Perl or awk.

You write that you don't want to use sort, because the data's size is larger than the machine's main memory size. Don't underestimate the implementation quality of the Unix sort command. Sort was used to handle very large volumes of data (think the original AT&T's billing data) on machines with 128k (that's 131,072 bytes) of memory (PDP-11). When sort encounters more data than a preset limit (often tuned close to the size of the machine's main memory) it sorts the data it has read in main memory and writes it into a temporary file. It then repeats the action with the next chunks of data. Finally, it performs a merge sort on those intermediate files. This allows sort to work on data many times larger than the machine's main memory.

Answer 9

I feel awk associative array is also handy in this case

$ awk '{count[$1]++}END{for(j in count) print j,count[j]}' ips.txt

A group by post here

http://unstableme.blogspot.com/2008/09/group-by-clause-functionality-in-awk.html

// Jadu

Answer 10

for summing up multiple fields, based on a group of existing fields, use the example below : ( replace the $1, $2, $3, $4 according to your requirements )

cat file

US|A|1000|2000 US|B|1000|2000 US|C|1000|2000 UK|1|1000|2000 UK|1|1000|2000 UK|1|1000|2000

awk 'BEGIN { FS=OFS=SUBSEP="|"}{arr[$1,$2]+=$3+$4 }END {for (i in arr) print i,arr[i]}' file

results in

US|A|3000 US|B|3000 US|C|3000 UK|1|9000