Duplicates in an unix text file based on multiple fields - unix

Question

I have a requirement to find duplicates based on three columns in a .txt file in unix which is delimited by ,.
Input:
a,b,c,d,e,f,gf,h
a,bd,cg,dd,ey,f,g,h
a,b,df,d,e,fd,g,h
a,b,ck,d,eg,f,g,h
Let's take we are finding dupliactes based on 1,2,5 fields.
Expected output:
a,b,c,d,e,f,gf,h
a,b,df,d,e,fd,g,h
Can anyone help to write a script for this or is there a command already available?
I tried like this:
awk -F, '!x[$1,$2,$3]++' file.txt but did not work

Answer 1

One way using awk:
awk -F, 'FNR==NR { x[$1,$2,$5]++; next } x[$1,$2,$5] > 1' a.txt a.txt
This is simple, but reads the file two times. On the first pass (FNR==NR), it maintains counts based on key fields. During the second pass, if prints the line if its key was found more than once.
Another way using awk:
awk -F, '{if (x[$1$2$5]) { y[$1$2$5]++; print $0; if (y[$1$2$5] == 1) { print x[$1$2$5] } } x[$1$2$5] = $0}' a.txt
Explanation:
1 awk -F,
2 '{if (x[$1$2$5])
3 { y[$1$2$5]++; print $0;
4 if (y[$1$2$5] == 1)
5 { print x[$1$2$5] }
6 } x[$1$2$5] = $0
7 }'
Line 2: If x has $1$2$5, this key was seen before, do steps 3-5
Line 3: Increment the count and print the line because it is a dup
Line 4: This means, We are seeing this key for the 2nd time, so we need to print the first line with this key. Last time we saw this key we did not know whether it was a dup or not. So we print the first line in step 5.
Line 6: Store the current line against the key so we can use it in step 2
Another way using sort, uniq and awk
Note: uniq command has an option '-f' to skip the specified number of fields before it starts comparison.
sort -t, -k1,1 -k2,2 -k5,5 a.txt | awk -F, 'BEGIN { OFS = " "} {print $0, $1, $2, $5}' | sed 's/,/ /g' | uniq -f7 -D | sed 's/ /,/g' | cut -d',' -f 1-7
This sorts based on fields 1,2,5. awk prints the original line and appends fields 1,2,5 . sed changes the delimiter because uniq does not have an option to specify delimiter. uniq skips first 7 fields and works on rest of the line and prints duplicate lines.

Answer 2

I had a similar issue
I needed to eliminate duplicate detail records while preserving flat file record formatting and seqence of the records.
The duplication caused by a time expansion of the date field in column 2 of the detail only.
Receiving system was reporting duplication on columns 4 and 5.
I cobbled together this quick hack to resolve it.
First read the file data into an array
Then we can read and manipulate the individual records (crudely with a counter) as demonstrated in this snippet integrating a case statement to logically treat the various record types.
Cheers!
readarray inrecs < [input file name]
filebase=echo "[input file name] | cut -d '.' -f1
i=1
for inrec in "${inrecs[#]}";do
field1=echo ${inrecs[$i-1]} | cut -d',' -f1
field2=echo ${inrecs[$i-1]} | cut -d',' -f2
field3=echo ${inrecs[$i-1]} | cut -d',' -f3
field4=echo ${inrecs[$i-1]} | cut -d',' -f4
field5=echo ${inrecs[$i-1]} | cut -d',' -f5
field6=echo ${inrecs[$i-1]} | cut -d',' -f6
field7=echo ${inrecs[$i-1]} | cut -d',' -f7
field8=echo ${inrecs[$i-1]} | cut -d',' -f8
case $field1 in
'H')
echo "$field1,$field2,$field3">${filebase}.new
;;
'D')
dupecount=0
dupecount=`zegrep -c -e "${field4},${field5}" ${infile}`
if [[ "$dupecount" -gt 1 ]];then
writtencount=0
writtencount=`zegrep -c -e "${field4},${field5}" ${filebase}.new`
if [[ "${writtencount}" -eq 0 ]];then
echo "$field1,$field2,$field3,$field4,$field5,$field6,$field7,$field8,">>${filebase}.new
fi
else
echo "$field1,$field2,$field3,$field4,$field5,$field6,$field7,$field8,">>${filebase}.new
fi
;;
'T')
dcount=`zegrep -c '^D' ${filebase}.new`
echo "$field1,$field2,$dcount,$field4">>${filebase}.new
;;
esac
((i++))
done