# interpNA: Interpolate missing values in a Time Indexed Series In tis: Time Indexes and Time Indexed Series

## Description

Calls `approxfun` or `splinefun` to interpolate missing values in a `tis` object.

## Usage

 `1` ```interpNA(x, method = "constant", useTimes = F, offset = 1, rule = 2, f = 0, ...) ```

## Arguments

 `x` a `tis` time series `method` One of c("constant", "linear", "fmm", "natural", "periodic"). Methods "constant" and "linear" call `approxfun`; the others call `splinefun`. `useTimes` if `TRUE`, use `time(x, offset)` (the decimal times of `x`) as the 'x' part of the (x, y) pairs used for interpolation. If `FALSE` (the default), use `ti(x)` (the integer time indices of `x`) as the 'x' part of the (x, y) pairs. `offset` if `useTimes` is `TRUE`, a number in the range [0,1] telling where in the periods represented by `ti(x)` to get the points for the 'x' parts of the (x, y) pairs. See the help for `jul` for a more detailed explanation of this parameter. `rule` For methods "constant" and "linear": an integer describing how interpolation is to take place outside the interval [`min(x)`, `max(x)`]. If `rule` is `1` then `NA`s are returned for such points and if it is `2`, the value at the closest data extreme is used. `f` For `method="constant"` a number between 0 and 1 inclusive, indicating a compromise between left- and right-continuous step functions. If `y0` and `y1` are the values to the left and right of the point then the value is `y0*(1-f)+y1*f` so that `f=0` is right-continuous and `f=1` is left-continuous. `...` Other arguments passed along to `approxfun` for methods "constant" and "linear".

## Details

Depending on the method specified, a call to either `approxfun` or `splinefun` is constructed with appropriate arguments and executed for each column of `x`. In the call to `approxfun` or `splinefun`, the time indices `ti(x)` (or the decimal times returned by `time(x, offset)`, if `useTimes` is `TRUE`) serve as the 'x' argument and the column values as the 'y' argument.

## Value

A `tis` object like `x` with `NA` values filled in by interpolated values.

`approxfun`, `splinefun`, `ti`