calculate the number of atoms in the PDB file - awk

Question

I would like to calculate the number of atoms for each residue in the pdb files. A PDB file looks as follows.The third column denotes the atoms and the fourth column denotes the residues.
ATOM 1 N ASN A 380 -0.011 22.902 -13.714 1.00 65.81 N
ATOM 2 CA ASN A 380 0.401 23.938 -12.714 1.00 65.53 C
ATOM 3 C ASN A 380 1.926 24.019 -12.595 1.00 64.48 C
ATOM 9 N THR A 381 2.553 24.693 -13.562 1.00 61.65 N
ATOM 10 CA THR A 381 4.006 24.848 -13.609 1.00 58.60 C
ATOM 16 N ILE A 382 5.156 22.716 -13.481 1.00 53.48 N
ATOM 17 CA ILE A 382 5.808 21.571 -12.830 1.00 49.47 C
ATOM 18 C ILE A 382 6.645 21.933 -11.584 1.00 45.24 C
ATOM 28 CB GLN A 383 8.735 24.763 -10.759 1.00 30.19 C
ATOM 29 CG GLN A 383 10.140 24.257 -11.037 1.00 29.17 C
ATOM 30 CD ASN A 384 10.397 23.975 -12.514 1.00 29.51 C
ATOM 31 OE1 ASN A 384 10.892 24.838 -13.237 1.00 30.67 O
I would like to get the output as follows
Total no:of ASN atoms - 5
Total no:of THR atoms - 2
Total no:of ILE atoms - 3
Total no:of GLN atoms - 2

Answer 1

This should do the job:
awk '{print $4}' <file> | sort | uniq -c | \
awk '{print "Total no:of", $2, "atoms -", $1}'
Or pure awk:
awk '{atom[$4]++;}
END{for (i in atom) {print "Total no:of", i, "atoms -", atom[i]} }' <file>
Output for both methods:
Total no:of GLN atoms - 2
Total no:of THR atoms - 2
Total no:of ASN atoms - 5
Total no:of ILE atoms - 3