Get Average of Numbers in a Column of HTML Table

This simple javascript calculates and displays the sum total of the 6th column in a table (which happens to have a header, then 12 rows of data, then a blank row at the bottom, where the sum of column 6 is displayed):

<script>
 function calcSum(){
      for (j=5;j<6;j++){
            sum=0
            for (i=1;i<13;i++) sum+=1*document.getElementById("numTable").rows[i].cells[j].innerHTML;
            document.getElementById("numTable").rows[i].cells[j].innerHTML=sum
     }
}
</script>

Instead of showing the sum of Column 6, however, I would like to show the mean average.  How would I modify the script to do that?
Randall-BAsked:
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Vel EousResearch & Development ManagerCommented:
<script>
 function calcSum(){
      for (j=5;j<6;j++){
            sum=0
            for (i=1;i<13;i++) sum+=1*document.getElementById("numTable").rows[i].cells[j].innerHTML;
            document.getElementById("numTable").rows[i].cells[j].innerHTML=sum/j // <------------
     }
}
</script>
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RoonaanCommented:
Shouldn't you need to divide by j*i?

document.getElementById("numTable").rows[i].cells[j].innerHTML
  = Math.round(sum/(j*i), 2)

-r-
0
Randall-BAuthor Commented:
Tchuki,
   Thanks, but dividing by j gives the wrong math average. For example, if each cell in the column has a "2" in it, the average should be 2.  But this modification gave an average of 4.8 .  Also, what if a cell is blank or simply has &nbsp; ? Then it gives an error of NaN.  How can I avoid that?
0
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RoonaanCommented:
<script>
 function calcSum(){
      for (j=5;j<6;j++){
            sum= 0;
            ints =0;
            for (i=1;i<13;i++) {
                var value = 1*document.getElementById("numTable").rows[i].cells[j].innerHTML;
                if(!isNaN(value)) { ints++; sum += value;}
             }
             document.getElementById("numTable").rows[i].cells[j].innerHTML
                 = ints > 0 ? sum : 0;
     }
}
</script>

-r-
0
Vel EousResearch & Development ManagerCommented:
Back to school for me ...  >.<
0
Randall-BAuthor Commented:
It seems to work if I divide by (i-1). I think that is because  i  is the number of data rows plus footer row.  Subtracting 1 gives number of data rows only. So this seems to work:  
     . . .     .innerHTML=sum/(i-1)
   I tried to put Roonaan's rounding feature into it, also, like this:
    . . .     .innerHTML=Math.round(sum/(i-1), 2)
but it is rounding to 1 digit, when I actually want two decimal places.  For example, it is rounding to 3 when the average is 2.77829102934 .  How can I round to 2.78 , instead?

     
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Randall-BAuthor Commented:
Roonan,
   Your script appears to add up a sum, instead of calculating an average.  But it works great for ignoring empty cells to avoid the NaN error.
    How would keep that great feature of working around empty cells, but calculate the average instead of the sum?  (And round to 2 decimal places)?  Based on my prior post, I think it has something to do with (i-1), but that would not account for empty cells, which would make the average come out wrong.  Thanks.
0
RoonaanCommented:
Yeah sorry, I was mixed up with other things. Please change:
= ints > 0 ? sum : 0;
To
= ints > 0 ? Math.round(sum/ints, 2) : 0;
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Randall-BAuthor Commented:
Roonaan,
    Good, that gives the average, but it is still rounding to an single digit (integer) instead of two decimal places.  For example, it rounded 2.346 to simply 3.  But I would like it to round to 2.35 .  How?  
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RoonaanCommented:
Then it might be possible that Round does not accept the ,2 argument.

Lets try:

= ints > 0 ? (Math.round(100*sum/ints, 2) / 100) : 0;

Regards

-r-
0

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Randall-BAuthor Commented:
Yes, that works.  So the complete script is:

<script>
 function calcSum(){
      for (j=5;j<6;j++){
            sum= 0;
            ints =0;
            for (i=1;i<13;i++) {
                var value = 1*document.getElementById("numTable").rows[i].cells[j].innerHTML;
                if(!isNaN(value)) { ints++; sum += value;}
             }
             document.getElementById("numTable").rows[i].cells[j].innerHTML = ints > 0 ? (Math.round(100*sum/ints, 2) / 100) : 0;

     }
}
</script>

Thanks!
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Michel PlungjanIT ExpertCommented:
or just

(sum/ints).toFixed(2)
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Randall-BAuthor Commented:
mplungjan:  Thanks. I also appreciate how that code makes it have 2 decimal places even if it would otherwise be a single digit.
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