One way to get around this is to do the following:
1. Determine the value of the first element in your data array that will be filtered.
2. Initialize an array whose elements are equal to value in step 1. For simplicity I always make the size of the array to be 100 elements.
3. Append this initialized array to the array you want filtered.
4. Filter the newly concatenated array.
5. After filtering, remove the first 100 elements.
6. Now plot the remaining elements of the array. The first point on the graph should be close in value to the second point...
Hope this helps.