Linearly interpolates missing values in a series.

Takes an expression containing dynamic numerical array as input, does linear interpolation for all instances of missing_value_placeholder, and returns the resulting array. If the beginning and end of the array contain missing_value_placeholder, then it's replaced with the nearest value other than missing_value_placeholder. This feature can be turned off. If the whole array consists of the missing_value_placeholder, the array is filled with constant_value, or 0 if not specified.


series_fill_linear(series, [ missing_value_placeholder [,fill_edges [, constant_value ]]])

Learn more about syntax conventions.


Name Type Required Description
series dynamic ✔️ An array of numeric values.
missing_value_placeholder scalar Specifies a placeholder for missing values. The default value is double(null). The value can be of any type that will be converted to actual element types. double(null), long(null) and int(null) have the same meaning.
fill_edges bool Indicates whether missing_value_placeholder at the start and end of the array should be replaced with nearest value. true by default. If set to false, then missing_value_placeholder at the start and end of the array will be preserved.
constant_value scalar Relevant only for arrays that entirely consist of null values. This parameter specifies a constant value with which to fill the series. Default value is 0. Setting this parameter it to double(null) preserves the null values.


A series linear interpolation of series using the specified parameters. If series contains only int or long elements, then the linear interpolation returns rounded interpolated values rather than exact ones.


  • If you create series using the make-series operator, specify null as the default value to use interpolation functions like series_fill_linear() afterwards. See explanation.
  • If missing_value_placeholder is double(null), or omitted, then a result may contain null values. To fill these null values, use other interpolation functions. Only series_outliers() supports null values in input arrays.
  • series_fill_linear() preserves the original type of the array elements.


let data = datatable(arr: dynamic)
    dynamic([null, 111.0, null, 36.0, 41.0, null, null, 16.0, 61.0, 33.0, null, null]), // Array of double    
    dynamic([null, 111, null, 36, 41, null, null, 16, 61, 33, null, null]), // Similar array of int
    dynamic([null, null, null, null])                                                   // Array with missing values only
| project
    without_args = series_fill_linear(arr),
    with_edges = series_fill_linear(arr, double(null), true),
    wo_edges = series_fill_linear(arr, double(null), false),
    with_const = series_fill_linear(arr, double(null), true, 3.14159)  


arr without_args with_edges wo_edges with_const
[null,111.0,null,36.0,41.0,null,null,16.0,61.0,33.0,null,null] [111.0,111.0,73.5,36.0,41.0,32.667,24.333,16.0,61.0,33.0,33.0,33.0] [111.0,111.0,73.5,36.0,41.0,32.667,24.333,16.0,61.0,33.0,33.0,33.0] [null,111.0,73.5,36.0,41.0,32.667,24.333,16.0,61.0,33.0,null,null] [111.0,111.0,73.5,36.0,41.0,32.667,24.333,16.0,61.0,33.0,33.0,33.0]
[null,111,null,36,41,null,null,16,61,33,null,null] [111,111,73,36,41,32,24,16,61,33,33,33] [111,111,73,36,41,32,24,16,61,33,33,33] [null,111,73,36,41,32,24,16,61,33,null,null] [111,111,74,38, 41,32,24,16,61,33,33,33]
[null,null,null,null] [0.0,0.0,0.0,0.0] [0.0,0.0,0.0,0.0] [0.0,0.0,0.0,0.0] [3.14159,3.14159,3.14159,3.14159]