title: Counting non-zero elements within each row and within each column of a 2D NumPy array
body: <p>I have a <code>NumPy</code> matrix that contains mostly non-zero values, but occasionally will contain a zero value. I need to be able to: </p>
  
  <ol>
  <li><p>Count the non-zero values in each row and put that count into a variable that I can use in subsequent operations, perhaps by iterating through row indices and performing the calculations during the iterative process.</p></li>
  <li><p>Count the non-zero values in each column and put that count into a variable that I can use in subsequent operations, perhaps by iterating through column indices and performing the calculations during the iterative process.</p></li>
  </ol>
  
  <p>For example, one thing I need to do is to sum each row and then divide each row sum by the number of non-zero values in each row, reporting a separate result for each row index.  And then I need to sum each column and then divide the column sum by the number of non-zero values in the column, also reporting a separate result for each column index.  I need to do other things as well, but they should be easy after I figure out how to do the things that I am listing here.</p>
  
  <p>The code I am working with is below. You can see that I am creating an array of zeros and then populating it from a <code>csv</code> file.  Some of the rows will contain values for all the columns, but other rows will still have some zeros remaining in some of the last columns, thus creating the problem described above.</p>
  
  <p>The last five lines of the code below are from another posting on this forum. These last five lines of code return a printed list of row/column indices for the zeros. However, I do not know how to use that resulting information to create the non-zero row counts and non-zero column counts described above.  </p>
  
  <pre><code>ANOVAInputMatrixValuesArray=zeros([len(TestIDs),9],float)
  j=0
  for j in range(0,len(TestIDs)):
      TestID=str(TestIDs[j])
      ReadOrWrite='Read'
      fileName=inputFileName
      directory=GetCurrentDirectory(arguments that return correct directory)
      inputfile=open(directory,'r')
      reader=csv.reader(inputfile)
      m=0
      for row in reader:
          if m&lt;9:
              if row[0]!='TestID':
                  ANOVAInputMatrixValuesArray[(j-1),m]=row[2]
                  m+=1
      inputfile.close()
  
  IndicesOfZeros = indices(ANOVAInputMatrixValuesArray.shape) 
  locs = IndicesOfZeros[:,ANOVAInputMatrixValuesArray == 0]
  pts = hsplit(locs, len(locs[0]))
  for pt in pts:
      print(', '.join(str(p[0]) for p in pt))
  </code></pre>
  
  <p>Can anyone help me with this?</p>