Heavy atom counts from an SD file

For each record from the benzodiazepine file, print the total number of heavy atoms in each record (that is, exclude hydrogens). You must get the data from the connection table and not from the tag data. (In particular, don't use PUBCHEM_HEAVY_ATOM_COUNT .)

The output is one output line per record, containing the count as an integer. If at all possible, show how to read directly from the gzip'ed input SD file. The first 5 heavy atom counts are 21, 24, 22, 22 and 22. A copy of the expected output is available for reference.

Some of the hydrogens in the data set have atomic weights of 2 or 3, which may cause difficulties for toolkits which convert ¹H hydrogens to implicit form while leaving ²H and ³H to explicit form. Please make sure your output agrees with the reference output.

CDK/Java

Save the code to "countHeavyAtoms.java" then do

javac countHeavyAtoms.java
   java -cp ./:$HOME/cdk-1.2.4.1.jar countHeavyAtoms > countHeavyAtoms.out

import java.io.*;
import org.openscience.cdk.interfaces.IChemObjectBuilder;
import org.openscience.cdk.io.iterator.IteratingMDLReader;
import org.openscience.cdk.Molecule;
import org.openscience.cdk.DefaultChemObjectBuilder;
import org.openscience.cdk.interfaces.IAtom;

public class countHeavyAtoms {	
    public static void main(String[] args) {	
        FileReader sdfile = null;
        try {
            /* CDK does not automatically understand gzipped files */
            sdfile = new FileReader(new File("benzodiazepine.sdf"));
        } catch (FileNotFoundException e) {
            System.err.println("benzodiazepine.sdf not found");
            System.exit(1);
        }

        IteratingMDLReader mdliter = new IteratingMDLReader(sdfile,
                                            DefaultChemObjectBuilder.getInstance());
        Molecule mol = null;
        while (mdliter.hasNext()) {
            mol = (Molecule) mdliter.next();
            int numHeavies = 0;
            for (IAtom a : mol.atoms()) {
                if (a.getAtomicNumber() > 1) {
                    numHeavies += 1;
                }
            }
            System.out.println(numHeavies);
        }
    }
}

CDK/Cinfony/Jython

from cinfony import cdk

manip = cdk.cdk.tools.manipulator.AtomContainerManipulator()
for mol in cdk.readfile("sdf", "benzodiazepine.sdf"):
    print len(manip.getHeavyAtoms(mol.Molecule))

Indigo/C++

#include "base_cpp/scanner.h"
#include "molecule/molecule.h"
#include "molecule/sdf_loader.h"
#include "molecule/molfile_loader.h"

int main (void)
{
   const char *filename = "benzodiazepine.sdf"; // you can use ".sdf.gz" as well

   try
   {
      FileScanner scanner(filename);
      SdfLoader loader(scanner);

      while (!loader.isEOF())
      {
         loader.readNext();
         Molecule mol;
         BufferScanner molscan(loader.data);
         MolfileLoader molload(molscan);
         molload.loadMolecule(mol, false);
            
         int i, heavy_count = 0;
         for (i = mol.vertexBegin(); i != mol.vertexEnd(); i = mol.vertexNext(i))
            if (mol.getAtom(i).label > ELEM_H)
               heavy_count++;

         printf("%d\n", heavy_count);
      }
   }
   catch (Exception &e)
   {
      fprintf(stderr, "error: %s\n", e.message());
      return -1;
   }

   return 0;
}

Instructions:

1. Unpack 'graph' and 'molecule' projects into some folder
2. Create 'utils' folder nearby
3. Paste the above code into utils/count_heavy.cpp file
4. Compile the file using the following commands:
   $ cd graph; make CONF=Release32; cd ..
   $ cd molecule; make CONF=Release32; cd ..
   $ cd utils
   $ gcc count_heavy.cpp -o count_heavy -O3 -m32 -I.. -I../common ../molecule/dist/Release32/GNU-Linux-x86/libmolecule.a ../graph/dist/Release32/GNU-Linux-x86/libgraph.a -lpthread -lstdc++
5. Run the program like that:
   $ ./count_heavy

OpenBabel/Python

import openbabel as ob

obconversion = ob.OBConversion()
obconversion.SetInFormat("sdf")

obmol = ob.OBMol()
notatend = obconversion.ReadFile(obmol, "benzodiazepine.sdf.gz")
while notatend:
    print obmol.NumHvyAtoms()
    # reuse the molecule for 0.3 seconds of savings vs. making an new one
    obmol.Clear()
    notatend = obconversion.Read(obmol)

OpenBabel/Pybel

This builds on and simplifies OpenBabel

import pybel

for mol in pybel.readfile("sdf", "benzodiazepine.sdf.gz"):
    print mol.OBMol.NumHvyAtoms()

OpenEye/Python

from openeye.oechem import *

ifs = oemolistream()
ifs.open("benzodiazepine.sdf.gz")
for mol in ifs.GetOEGraphMols():
    print OECount(mol, OEIsHeavy())
    # Can't use
    #    print mol.NumAtoms()
    # because the input structure contains explicit hydrogens.

RDKit/Python

I could also have iterated over the atoms and only counted the non-hydrogen ones, but I doubt that would be any faster or elegant.

from rdkit import Chem

# RDKit does not seem to support gzip'ed SD files
suppl = Chem.SDMolSupplier("benzodiazepine.sdf")
heavy_patt = Chem.MolFromSmarts("[!#1]")

for mol in suppl:
    print len(mol.GetSubstructMatches(heavy_patt))

The method "mol.GetNumAtoms()" is supposed to report only the non-hydrogen counts, but actually reports the number of explicit atoms in the molecular graph.

RDKit/Cinfony/Python

from cinfony import rdk

for mol in rdk.readfile("sdf", "benzodiazepine.sdf"):
    print mol.calcdesc(['HeavyAtomCount'])['HeavyAtomCount']

Unix command-line

It is possible to do this on the Unix command-line using a single (very long) line. To make it easier to understand I've written it using an awk script named 'heavy_atom_counts.awk'. Use it as:

gzcat benzodiazepine.sdf.gz | awk -f heavy_atom_counts.awk

# This file is named "heavy_atom_counts.awk"
# Check track of the line number in the record
{lineno += 1}

# Get the atom counts from the record
lineno == 4 { num_atoms = int(substr($0, 1, 3)); num_hydrogens = 0}

# Count the number of hydrogens
4 < lineno && lineno <= 4+num_atoms && substr($0, 32, 2) == "H " {num_hydrogens++}

# And the end of the record, print the number of heavy atoms and reset
/^\$\$\$\$/ {print num_atoms - num_hydrogens; lineno = 0}