Performs a backward fill interpolation of missing values in a series.

An expression containing dynamic numerical array is the input. The function replaces all instances of missing_value_placeholder with the nearest value from its right side (other than missing_value_placeholder), and returns the resulting array. The rightmost instances of missing_value_placeholder are preserved.


series_fill_backward(x[, missing_value_placeholder])

  • Will return series x with all instances of missing_value_placeholder filled backwards.


  • x: dynamic array scalar expression, which is an array of numeric values.
  • missing_value_placeholder: this optional parameter specifies a placeholder for missing values. The default value is double(null).


  • Specify null as the default value to apply any interpolation functions after make-series:
make-series num=count() default=long(null) on TimeStamp from ago(1d) to ago(1h) step 1h by Os, Browser
  • The missing_value_placeholder can be of any type that will be converted to actual element types. Both double(null), long(null) and int(null) have the same meaning.
  • If missing_value_placeholder is double(null), (or omitted, which have the same meaning) then a result may contain null values. To fill these null values, use other interpolation functions. Currently only series_outliers() support null values in input arrays.
  • The function preserves original type of array elements.


let data = datatable(arr: dynamic)
| project arr, 
          fill_forward = series_fill_backward(arr)

arr fill_forward
[111,null,36,41,null,null,16,61,33,null,null] [111,36,36,41,16, 16,16,61,33,null,null]

Use series_fill_forward or series-fill-const to complete interpolation of the above array.