The only place I would think that random spacing would be required if there
was a timer stamp on each row where data would be placed in the spreadsheet
everytime the data changed, but you wanted to plot the data at specifc
timestamps.

I would use the tiomestamp to help select the desire rows.  

The best way to randomly select data is to add three additional columns to
your data.  One is an index which is to number the rows from 1 to last row in
order.  The reason for this is to return the data to the original order.  the
add random numbers to a second new column.  Sort by random number.  Then mark
the number of rows you want to sample in the third new column.  If you have
100 rows of data and you want to sample 15 random pieces of data then add a 1
to the third new column.  then use the index column to return the data to the
original order.  then you can modify original UDF code to pass the third new
column to use to select which rows of data to use.

If you need help let me know.