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awk : search last index in specific column

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# 1  
Old 10-29-2013
awk : search last index in specific column
I am trying to search a given text in a file and find its last occurrence index. The task is to append the searched index in the same file but in a separate column. I am able to accomplish the task partially and looking for a solution.

Following is the detailed description:

names_file.txt
Code:
111|lkasjdfaaa|555|tarun trehan
111|aaa|55765|vikram batra
111|aaa|555|allzhere blog
65876111|aaa|555|allzhere android apps
111|hhhaaa|555|allzhere on facebook
111|aaa|555|contact updater utility
111|aaa|444555|help me

Assuming, i am trying to search last occurrence index of "n" in the name i.e. my last column of file. So, the output file should be as following where the last column is representing the last index of "n" in the name column:

Output File :
Code:
111|lkasjdfaaa|555|tarun trehan|12
65876111|aaa|555|allzhere android apps|11
111|hhhaaa|555|allzhere on facebook|11
111|aaa|555|contact updater utility|3

I tried the following command:

Code:
cat names_file.txt | awk -F"|" '{print $4}' | awk -F"n" 'NF>1{print $0"|"length($0) - length($NF)}'

It gives me the following results:
Code:
tarun trehan|12
allzhere android apps|11
allzhere on facebook|11
contact updater utility|3

How can i fetch the rest of the columns first awk and still scan the 4th column only. I want the desired output described above.
Last edited by vbe; 10-29-2013 at 11:28 AM.. Reason: code tags... also for data!
# 2  
Old 10-29-2013
Using awk match function:
Code:
awk -F\| '
        {
                for ( i = 1; i <= NF; i++ )
                {
                        n = match ( $i, /n[^n]*$/ )
                }
                if ( n )
                        print $0, n
        }
' OFS=\| names_file.txt

This User Gave Thanks to Yoda For This Post:
RavinderSingh13
# 3  
Old 10-29-2013
Excellent Yoda, I am big fan of you. Could you please explain me the code with the
Code:
match

please.


Thanks,
R. Singh
# 4  
Old 10-29-2013
Syntax:
Code:
match(string, regexp)

The match function searches the string, for the longest, leftmost substring matched by the regexp. It returns the character position, or index

Since match function searches the leftmost, I used regexp /n[^n]*$/ to match the last character n

Refer: GNU awk string functions
# 5  
Old 10-29-2013
Yoda,

Thanks for your reply. Appreciate your inputs.
I have the following queries:

1. i am getting a syntax error around the
Code:
n = match ( $i, /n[^n]*$/ )

..may be i am not pasting the character correctly.

2. This code is scanning all variables and i would like to search only the 4th column. I think i can do that by adding a if clause for i==4.

3. I am onto text mining a huge file set i.e. 10 million records. Is line by line scanning a viable option ??
# 6  
Old 10-29-2013
1. i am getting a syntax error around the n = match ( $i, /n[^n]*$/ )..may be i am not pasting the character correctly.
Use nawk instead if you are using SunOS or Solaris

2. This code is scanning all variables and i would like to search only the 4th column. I think i can do that by adding a if clause for i==4.
Yes, remove the for loop and put $4 instead: n = match ( $4, /n[^n]*$/ )

3. I am onto text mining a huge file set i.e. 10 million records. Is line by line scanning a viable option ??
Yes.
# 7  
Old 10-29-2013
Quote:
Using awk match function:

Code:
awk -F\| ' { for ( i = 1; i <= NF; i++ ) { n = match ( $i, /n[^n]*$/ ) } if ( n ) print $0, n }' OFS=\| names_file.txt


Hi Yoda,

Sorry to bother you, I have tried searching the match expression given by you in code but was not able to under stand it could you please exaplain it.


Code:
n = match ( $i, /n[^n]*$/ )

Thanks,
R. Singh
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