Best way to simulate "group by" from bash?
BashScriptingBash Problem Overview
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. :-)
Bash Solutions
Solution 1 - Bash
sort ip_addresses | uniq -c
This will print the count first, but other than that it should be exactly what you want.
Solution 2 - Bash
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.
Solution 3 - Bash
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
US|A|3000
US|B|3000
US|C|3000
UK|1|9000
Solution 4 - Bash
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.
Solution 5 - Bash
cat ip_addresses | sort | uniq -c | sort -nr | awk '{print $2 " " $1}'
this command would give you desired output
Solution 6 - Bash
Solution ( group by like mysql)
grep -ioh "facebook\|xing\|linkedin\|googleplus" access-log.txt | sort | uniq -c | sort -n
Result
3249 googleplus
4211 linkedin
5212 xing
7928 facebook
Solution 7 - Bash
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...
Solution 8 - Bash
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.
Solution 9 - Bash
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
Solution 10 - Bash
Most of the other solutions count duplicates. If you really need to group key value pairs, try this:
Here is my example data:
find . | xargs md5sum
fe4ab8e15432161f452e345ff30c68b0 a.txt
30c68b02161e15435ff52e34f4fe4ab8 b.txt
30c68b02161e15435ff52e34f4fe4ab8 c.txt
fe4ab8e15432161f452e345ff30c68b0 d.txt
fe4ab8e15432161f452e345ff30c68b0 e.txt
This will print the key value pairs grouped by the md5 checksum.
cat table.txt | awk '{print $1}' | sort | uniq | xargs -i grep {} table.txt
30c68b02161e15435ff52e34f4fe4ab8 b.txt
30c68b02161e15435ff52e34f4fe4ab8 c.txt
fe4ab8e15432161f452e345ff30c68b0 a.txt
fe4ab8e15432161f452e345ff30c68b0 d.txt
fe4ab8e15432161f452e345ff30c68b0 e.txt
Solution 11 - Bash
GROUP BY under [tag:bash]
Regarding this SO thread, there are lot of different answer regarding different needs.
1. Counting IP as SO request (GROUP BY IP address).
Of course, working on a huge file could be done as already answered, by using
sort <ip_addresses | unic c
But for small bunch of address, if you need to do this kind of operation many time, using a pure [tag:bash] function could be more efficient.
Pure [tag:bash] (no fork!)
There is a way, using a [tag:bash] function. This way is very quick as there is no fork!...
... While bunch of ip addresses stay small!
countIp () {
local -a _ips=(); local _a
while IFS=. read -a _a ;do
((_ips[_a<<24|${_a1}<<16|${_a[2]}<<8|${_a[3]}]++))
done
for _a in ${!_ips[@]} ;do
printf "%.16s %4d\n"
$(($_a>>24)).$(($_a>>16&255)).$(($_a>>8&255)).$(($_a&255)) ${_ips[_a]}
done
}
Note: IP addresses are converted to 32bits unsigned integer value, used as index for array. This use simple bash arrays, not associative array (wich is more expensive)!
time countIp < ip_addresses
10.0.10.1 3
10.0.10.2 1
10.0.10.3 1
real 0m0.001s
user 0m0.004s
sys 0m0.000s
time sort ip_addresses | uniq -c
3 10.0.10.1
1 10.0.10.2
1 10.0.10.3
real 0m0.010s
user 0m0.000s
sys 0m0.000s
On my host, doing so is a lot quicker than using forks, upto approx 1'000 addresses, but take approx 1 entire second when I'll try to sort'n count 10'000 addresses.
2. GROUP BY duplicates
By using checksum you could indentfy duplicate files somewhere:
find . -type f -exec sha1sum {} + | sort | sed ' :a; $s/^[^ ]+ +//; N; s/^([^ ]+) +([^ ].)\n\1 +([^ ].)$/\1 \2\o11\3/; ta; s/^[^ ]+ +//; P; D; ba '
This will print all duplicates, by line, separated by Tabulation ($'\t' or octal 011 ou could change /\1 \2\o11\3/; by /\1 \2|\3/; for using | as separator).
./b.txt ./e.txt ./a.txt ./c.txt ./d.txt
Could be written as (with | as separator):
find . -type f -exec sha1sum {} + | sort | sed ':a;$s/^[^ ]\+ \+//;N;
s/^\([^ ]\+\) \+\([^ ].*\)\n\1 \+\([^ ].*\)$/\1 \2|\3/;ta;s/^[^ ]\+ \+//;P;D;ba'
Pure [tag:bash] way
By using nameref, you could build bash arrays holding all duplicates:
declare -iA sums='()' while IFS=' ' read -r sum file ;do declare -n list=LST$sum list+=($file) sums[$sum]+=1 done < <( find . -type f -exec sha1sum {} + )
From there, you have a bunch of arrays holding all duplicates file name as separated element:
for i in ${!sums[@]};do declare -n list=LST$i printf "%d %d %s\n" ${sums[$i]} ${#list[@]} "${list[*]}" done
This may output something like:
2 2 ./e.txt ./b.txt
3 3 ./c.txt ./a.txt ./d.txt
Where count of files by md5sum (${sums[$shasum]}) match count of element in arrays ${_LST_ShAsUm[@]}.
for i in ${!sums[@]};do declare -n list=LST$i echo ${list[@]@A} done declare -a _LST_22596363b3de40b06f981fb85d82312e8c0ed511=([0]="./e.txt" 1="./b.txt") declare -a _LST_f572d396fae9206628714fb2ce00f72e94f2258f=([0]="./c.txt" 1="./a.txt" [2]="./d.txt")
Note that this method could handle spaces and special characters in filenames!
3. GROUP BY columns in a table
As efficient sample using awk was provided by Anonymous, here is a pure [tag:bash] solution.
So you want to sumarize columns 3 to last column and group by columns 1 and 2, having table.txt looking like
> US|A|1000|2000 > US|B|1000|2000 > US|C|1000|2000 > UK|1|1000|2000 > UK|1|1000|2000|3000 > UK|1|1000|2000|3000|4000
For not too big tables, you could:
myfunc() { local -iA restabl='()'; local IFS=+ while IFS=| read -ra ar; do restabl["${ar[0]}|${ar1}"]+="${ar[*]:2}" done for i in ${!restabl[@]} ;do printf '%s|%s\n' "$i" "${restabl[$i]}" done }
Could ouput something like:
myfunc
Solution 12 - Bash
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.
Solution 13 - Bash
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.
Solution 14 - Bash
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