slope formula only for cells that contain value

[jebagr]

Hi there

I have a huge number of rows with sales data. I want to use the slope formula to determine the trend. However the sales data is full of gaps like this example.

[TABLE="width: 500"]
<tbody>[TR]
[TD]3[/TD]
[TD]4[/TD]
[TD]5[/TD]
[TD]8[/TD]
[TD]0[/TD]
[TD]2[/TD]
[TD]8[/TD]
[/TR]
[TR]
[TD]N/A[/TD]
[TD]5[/TD]
[TD]8[/TD]
[TD]1[/TD]
[TD]9[/TD]
[TD]7[/TD]
[TD]1[/TD]
[/TR]
[TR]
[TD]5[/TD]
[TD]N/A[/TD]
[TD]8[/TD]
[TD]7[/TD]
[TD]3[/TD]
[TD]8[/TD]
[TD]9[/TD]
[/TR]
[TR]
[TD]3[/TD]
[TD]8[/TD]
[TD]9[/TD]
[TD]5[/TD]
[TD]3[/TD]
[TD]1[/TD]
[TD]N/A[/TD]
[/TR]
[TR]
[TD]N/A[/TD]
[TD]3[/TD]
[TD]1[/TD]
[TD]6[/TD]
[TD]9[/TD]
[TD]2[/TD]
[TD]N/A[/TD]
[/TR]
</tbody>[/TABLE]

Since the data doesn't start and end at the same columns all the time, I was wondering if anybody knows a way to solve this (for example in row 1 I want to use everything, in row 3 I only want to use 8-7-3-8-9, in row 5 I want to use 3-1-6-9-2)

Thanks!