To implement linear interpolation with sparse data, create following calculated fields and edit table calculations.

Create Calculated Fields

Select Analysis > Create Calculated Field... to create the following calculation fields

• 1_existing data INDEX
  IF NOT ISNULL(SUM([Measure])) THEN INDEX() END
  
  
• 2_missing data PREVIOUS INDEX
  IFNULL([1_existing data INDEX],PREVIOUS_VALUE(0))
  
  
• 3_missing data NEXT INDEX
  IFNULL([1_existing data INDEX],PREVIOUS_VALUE(0))
  
  
• 4_missing data INDEX difference
  [3_missing data NEXT INDEX]-[2_missing data PREVIOUS INDEX]
  
  
• 5_missing data INDEX difference to current spot
  INDEX()-[2_missing data PREVIOUS INDEX]
  
  
• 6_missing data PREVIOUS Measure
  IFNULL(SUM([Measure]),PREVIOUS_VALUE(0))
  
  
• 7_missing data NEXT Measure
  IFNULL(SUM([Measure]),PREVIOUS_VALUE(0)) 
  
  
• 8_missing data VALUE difference
  [7_missing data NEXT Measure]-[6_missing data PREVIOUS Measure]
  
  
• 9_Linear Interpolation
  IFNULL(LOOKUP(SUM([Measure]),0),
[8_missing data VALUE difference]/[4_missing data INDEX difference]*[5_missing data INDEX difference to current spot]+[6_missing data PREVIOUS Measure]
)

Build the view

1. Drag Dimension to the Columns shelf
2. Drag 9_Linear Interpolation to the Rows shelf

Edit Table Calculations

1. Right-click 9_Linear Interpolation on the Rows shelf, and select Edit Table Calculation...
2. For Nested Calculations, choose 7_missing data NEXT Measure
3. For Compute Using, choose Specific Dimensions, and check Dimension
4. For Sort order, choose
   Custom
   Dimension Minimum
   Descending
5. For Nested Calculations, choose 3_missing data NEXT INDEX
6. For Compute Using, choose Specific Dimensions, and check Dimension
7. For Sort order, choose
   Custom
   Dimension Minimum
   Descending
8. Close the Table Calculation dialog box