R: Handling Missing Time Series Values

na {timeSeries}

R Documentation

Handling Missing Time Series Values

Description

Functions for handling missing values in 'timeSeries' objects or in objects which can be transformed into a vector or a two dimensional matrix.

The functions are listed by topic.

`na.omit`	Handles NAs,
`removeNA`	Removes NAs from a matrix object,
`substituteNA`	substitute NAs by zero, the column mean or median,
`interpNA`	interpolates NAs using R's "approx" function.

Usage

## S4 method for signature 'timeSeries'
na.omit(object, method = c("r", "s", "z", "ir", "iz", "ie"), 
    interp = c("before", "linear", "after"), ...)

removeNA(x, ...)
substituteNA(x, type = c("zeros", "mean", "median"), ...)
interpNA(x, method = c("linear", "before", "after"), ...)

Arguments

`interp, type`	[nna.omit][substituteNA] - Three alternative methods are provided to remove NAs from the data: `type="zeros"` replaces the missing values by zeros, `type="mean"` replaces the missing values by the column mean, `type="median"` replaces the missing values by the the column median.
`method`	[na.omit] - Specifies the method how to handle NAs. One of the applied vector strings: `method="s"` na.rm = FALSE, skip, i.e. do nothing, `method="r"` remove NAs, `method="z"` substitute NAs by zeros, `method="ir"` interpolate NAs and remove NAs at the beginning and end of the series, `method="iz"` interpolate NAs and substitute NAs at the beginning and end of the series, `method="ie"` interpolate NAs and extrapolate NAs at the beginning and end of the series, [interpNA] - Specifies the method how to interpolate the matrix column by column. One of the applied vector strings: `method="linear"`, `method="before"` or `method="after"`. For the interpolation the function `approx` is used.
`object`	an object of class("timeSeries").
`x`	a numeric matrix, or any other object which can be transformed into a matrix through `x = as.matrix(x, ...)`. If `x` is a vector, it will be transformed into a one-dimensional matrix.
`...`	arguments to be passed to the function `as.matrix`.

Details

Missing Values in Price and Index Series:

Applied to timeSeries objects the function removeNA just removes rows with NAs from the series. For an interpolation of time series points one can use the function interpNA. Three different methods of interpolation are offered: "linear" does a linear interpolation, "before" uses the previous value, and "after" uses the following value. Note, that the interpolation is done on the index scale and not on the time scale.

Missing Values in Return Series:

For return series the function substituteNA may be useful. The function allows to fill missing values either by method="zeros", the method="mean" or the method="median" value of the appropriate columns.

Note

The functions removeNA, substituteNA and interpNA are older implementations. Please use in all cases if possible the new function na.omit.

References

Troyanskaya O., Cantor M., Sherlock G., Brown P., Hastie T., Tibshirani R., Botstein D., Altman R.B., (2001); Missing Value Estimation Methods for DNA microarrays Bioinformatics 17, 520–525.

Examples

## Create a Matrix -
   X = matrix(rnorm(100), ncol = 5)
   
## Replace a Single NA Inside - 
   X[3, 5] = NA
   
## Replace Three in a Row Inside - 
   X[17, 2:4] = c(NA, NA, NA)
   
## Replace Three in a Column Inside - 
   X[13:15, 4] = c(NA, NA, NA)
   
## Replace Two at the Right Border - 
   X[11:12, 5] = c(NA, NA)
   
## Replace One in the Lower Left Corner - 
   X[20, 1] = NA
   print(X)
     
## Remove Rows with NAs - 
   removeNA(X)
   
## Subsitute NA's by Zeros or Column Mean - 
   substituteNA(X, type = "zeros")
   substituteNA(X, type = "mean")
   
## Interpolate NA's Linearily - 
   interpNA(X, method = "linear")
   # Note the corner missing value cannot be interpolated!
   
## Take Previous Values in a Column - 
   interpNA(X, method = "before")
   # Also here, the corner value is excluded

[Package timeSeries version 2160.95 Index]