Filtering using awk returns empty files - awk

Question

I have a similar problem to this question: How to do filtering of multiple files in a directory using awk?
The solution in the answers of the question above does not work for me.
I have tab-delimited txt files (all in folder Observation_by_pracid). For each file, I want to create a new file that only contains rows with a specific value in column $9 (medcodeid). The specific values are to be found in medicalcode_list.txt.
There is no error, however it returns only empty files.
Codelist
medcodeid
2576
3199
Format of input files
patid consid ... medcodeid
500470520002 3062539302 ... 2576
951924020002 3062538414 ... 310803013
503478020002 3061587464 ... 257619018
951924020002 3062537807 ... 55627011
503576720002 3062537720 ... 3199
Desired output
patid consid ... medcodeid
500470520002 3062539302 ... 2576
503576720002 3062537720 ... 3199
My code
mkdir HBA1C_observation_bypracid
awk '
NR==FNR {mlist[$1]; next }
FNR==1 {close(out); out="HBA1C_observation_bypracid/HBA1C_" FILENAME }
($9 in mlist) { print > out }
' PATH/medicalcode_list.txt *.txt
Solution
mkdir HBA1C_observation_bypracid
awk '
BEGIN{ FS=OFS="\t" }
NR==FNR {mlist[$1]; next }
FNR==1 {close(out); out="HBA1C_observation_bypracid/HBA1C_" FILENAME }
($9 in mlist) { print > out }
' PATH/medicalcode_list.txt *.txt
Adding "BEGIN..." solved my problem.

Answer 1

You can join two files on a column using join.
Files must be sorted on the joined column. To perform a numerical sort on a column, use sort this way, where N is the column number:
sort -kN -n FILE
You also need to get ride of the first line (column names) of each files. You can use tail command the way below, where N is the number of line from which you want to output the content (so 2nd line):
tail -n +N
... But still need to display the column values:
head -n 1 FILE
To join two files f1 and f2, on the fields c1 of f1 and c2 of f2, and output fields y of files x:
join -1 c1 -2 c2 f1 f2 -o "x.y, x.y"
Working sample:
head -n 1 input_file
for input_file in *.txt ; do
join -1 1 -2 9 -o "2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9" \
<(tail -n +2 PATH/medicalcode_list.txt | sort -k1 -n) \
<(tail -n +2 "$input_file" | sort -k3 -n)
done
Result (for the input file you gave):
patid consid ... medcodeid
500470520002 3062539302 ... 2576
503576720002 3062537720 ... 3199
Note: the column names arent aligned with the values. Don't know if it's a prerequisite. You can format the display with printf command.

Answer 2

Personally I think it would be simpler to loop over in the shell (understanding that this will reread the code list more than once), with a simpler awk function that you should be able to test and debug. Something like:
for file in *.txt; do
awk 'FNR == NR { mlist[$1] } FNR != NR && ($9 in mlist) { print }' \
PATH/medicalcode_list.txt "$file" > HBA1C_observation_bypracid/HBA1C_"$file"
done
You should be able to start without the redirection to make sure that for a single file, you get the results printed to the terminal that you were expected. If you don't there might be some incorrect assumption about the files.
Another option would be to write a separate awk script that writes the code to hard-code the list in another awk script. Also gives the advantage to check the contents of the variable mlist.
printf 'BEGIN {\n%s\n}\n $9 in mlist { print }' \
"$(awk '{ print "mlist[" $1 "]" }' PATH/medicalcode_list.txt)" > filter.awk
for file in *.txt; do
awk -f filter.awk "$file" > HBA1C_observation_bypracid/HBA1C_"$file"
done