summarizing the contents of a text file to an other one using awk - awk

Question

I have a big text file with 2 tab separated fields. as you see in the small example every 2 lines have a number in common. I want to summarize my text file in this way.
1- look for the lines that have the number in common and sum up the second column of those lines.
small example:
ENST00000054666.6 2
ENST00000054666.6_2 15
ENST00000054668.5 4
ENST00000054668.5_2 10
ENST00000054950.3 0
ENST00000054950.3_2 4
expected output:
ENST00000054666.6 17
ENST00000054668.5 14
ENST00000054950.3 4
as you see the difference is in both columns. in the 1st column there is only one repeat of each common and without "_2" and in the 2nd column the values is sum up of both lines (which have common number in input file).
I tried this code but does not return what I want:
awk -F '\t' '{ col2 = $2, $2=col2; print }' OFS='\t' input.txt > output.txt
do you know how to fix it?

Answer 1

Solution 1st: Following awk may help you on same.
awk '{sub(/_.*/,"",$1)} {a[$1]+=$NF} END{for(i in a){print i,a[i]}}' Input_file
Solution 2nd: In case your Input_file is sorted by 1st field then following may help you.
awk '{sub(/_.*/,"",$1)} prev!=$1 && prev{print prev,val;val=""} {val+=$NF;prev=$1} END{if(val){print prev,val}}' Input_file
Use > output.txt at the end of the above codes in case you need the output in a output file too.

Answer 2

If order is not a concern, below may also help :
awk -v FS="\t|_" '{count[$1]+=$NF}
END{for(i in count){printf "%s\t%s%s",i,count[i],ORS;}}' file
ENST00000054668.5 14
ENST00000054950.3 4
ENST00000054666.6 17
Edit :
If the order of the output does matter, below approach using a flag helps :
$ awk -v FS="\t|_" '{count[$1]+=$NF;++i;
if(i==2){printf "%s\t%s%s",$1,count[$1],ORS;i=0}}' file
ENST00000054666.6 17
ENST00000054668.5 14
ENST00000054950.3 4