awk find and replace variable file2 into file1 when matched

Question

Tried couple of answers from similar questions but not quite getting correct results. Trying to search second file for variable and replace with second variable if there, otherwise keep original...

File1.txt

a
2
c
4
e
f

File2.txt

2 b
4 d

Wanted Output.txt

a
b
c
d
e
f

So far what I have seems to sort of work, but anywhere the replacement is happening I'm getting a blank row instead of the new variable... Current Output.txt

a

c

e
f

Curent code....

awk -F'\t' 'NR==FNR{a[$1]=$2;next} {print (($1 in a) ? a[$1] : $1)}' file2.txt file1.txt > output.txt

Also tried and got same results...

awk -F'\t' 'NR==FNR{a[$1]=$2;next} {$1 = a[$1]}1' file2.txt file1.txt > output.txt

Sorry first wrote incorrectly..fixed the key value issue.

Did try what you did, still not getting missing in output.txt

awk -F'\t' 'NR==FNR{a[$1]=$2;next} $1 in a{$1 = a[$1]}1' file2.txt file1.txt > output.txt

Also just a comment, these files are about 2million lines for file1 and 1.5million for file2. I only want to change file1 when match is found in file2. I've checked number of lines in my output file to make sure it is correct, which it is, but when I check some that I know should have been changed, that's when I found they are blank lines instead of having the new variable. So it seems to be finding the variable that matches, but then replacing it with nothing. — Catherine
– Catherine, Commented Oct 24, 2016 at 14:49
fixed the parenthesis, was in my actual code, so not what's causing the problem. Thanks. — Catherine
– Catherine, Commented Oct 24, 2016 at 18:47
No it's not. It's gotta be something with your data. Codes are fine. Double tabs or something. Or a tab and a space. — James Brown
– James Brown, Commented Oct 24, 2016 at 18:57

karakfa · Accepted Answer · 2016-10-24 14:29:37Z

1

your key value pair is not right... $1 is the key, $2 is the value.

$ awk -F'\t' 'NR==FNR{a[$1]=$2;next} $1 in a{$1=a[$1]}1' file.2 file.1
a
b
c
d
e
f

answered Oct 24, 2016 at 14:29

karakfa

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5 Comments

Catherine Over a year ago

Sorry, I wrote it in here for more simplicity and mixed the key value up. I just tried what you wrote and still giving me missing values...and a little confused as how

Catherine Over a year ago

'$1 in a{$1=a[$1]}' is different that what I wrote above?

karakfa Over a year ago

yes, you wrote $1 = a[$2], which is also not correct.

Catherine Over a year ago

Hi, Sorry. Because I had originally mixed up the key value above, I thought you're {1=a[$1]} was different than mine because of that, but it's not. I just changed that one part and it works. Can you explain that part. I thought it was saying make column 1 of file1 now equal the value of a[$2] from file2?

karakfa Over a year ago

Think of array "a" as a lookup. You are looking for the value stored for the key, which is $1.

VIPIN KUMAR · Accepted Answer · 2019-01-05 06:18:17Z

0

try below solution -

awk 'NR==FNR{a[$1]=$NF;next} {print (a[$NF]?a[$NF]:$1)}' file2.txt file1.txt

a
b
c
d
e
f

edited Jan 5, 2019 at 6:18

answered Oct 24, 2016 at 20:50

VIPIN KUMAR

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