---
title: "zoo Reference Card"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{zoo Reference Card}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteDepends{zoo}
  %\VignetteKeywords{irregular time series, ordered observations, time index}
  %\VignettePackage{zoo}
---

## Creation

* [zoo(x, order.by)](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Creation of a `"zoo"` object from the observations `x` (a vector or a matrix) and an index `order.by` by which the observations are ordered.

  For computations on arbitrary index classes, methods to the following generic functions are assumed to work: combining `c()`, querying length `length()`, subsetting `[`, ordering `ORDER()` and value matching `MATCH()`. For pretty printing an `as.character` and/or `index2char` method might be helpful.


## Creation of regular series

* [zoo(x, order.by, freq)](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Works as above but creates a `"zooreg"` object which inherits from `"zoo"` if the frequency `freq` complies with the index `order.by`. An `as.numeric` method has to be available for the index class.
* [zooreg(x, start, end, freq)](https://zeileis.codeberg.page/zoo/man/zooreg.html):
  Creates a `"zooreg"` series with a numeric index as above and has (almost) the same interface as `ts()`.                              |


## Standard methods

* [plot](https://zeileis.codeberg.page/zoo/man/plot.zoo.html):
  Plotting. Alternatives:
  [xyplot](https://zeileis.codeberg.page/zoo/man/xyplot.zoo.html) (`lattice`),
  [autoplot](https://zeileis.codeberg.page/zoo/man/ggplot2.zoo.html) (`ggplot2`),
  [tinyplot](https://zeileis.codeberg.page/zoo/man/tinyplot.zoo.html).
* [lines](https://zeileis.codeberg.page/zoo/man/plot.zoo.html):
  Adding a `"zoo"` series to a plot.
* [print](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Printing.
* [summary](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Summarizing (column-wise).
* [str](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Displaying structure of `"zoo"` objects.
* [head, tail](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Head and tail of `"zoo"` objects.


## Import/export

* [read.zoo](https://zeileis.codeberg.page/zoo/man/read.zoo.html):
  Reads `"zoo"` objects from text files, e.g., in CSV format (comma-separated values).
* [write.zoo](https://zeileis.codeberg.page/zoo/man/read.zoo.html):
  Writes `"zoo"` objects to text files such, e.g., in CSV format.


## Coercion

* [as.zoo](https://zeileis.codeberg.page/zoo/man/as.zoo.html):
  Coercion to `"zoo"` is available for objects of class `"ts"`, `"xts"`, `"timeSeries"`, and many others.
* [as.*class*.zoo](https://zeileis.codeberg.page/zoo/man/as.zoo.html):
  Coercion from `"zoo"` to other classes. Includes methods for *class* in `"matrix"`, `"vector"`, `"data.frame"`, `"list"`, `"ts"`, `"xts"`, `"timeSeries"`, and several others.
* [is.zoo](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Querying wether an object is of class `"zoo"`.


## Merging and binding

* [merge](https://zeileis.codeberg.page/zoo/man/merge.zoo.html):
  Union, intersection, left join, right join along indexes.
* [cbind](https://zeileis.codeberg.page/zoo/man/merge.zoo.html):
  Column binding along the intersection of the index.
* [c, rbind](https://zeileis.codeberg.page/zoo/man/merge.zoo.html):
  Combining/row binding (indexes may not overlap).
* [aggregate](https://zeileis.codeberg.page/zoo/man/aggregate.zoo.html):
  Compute summary statistics along a coarser grid of indexes


## Mathematical operations

* [Ops](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Group generic functions performed along the intersection of indexes.
* [t](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Transposing (coerces to `"matrix"` before).
* [cumsum](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Compute (columnwise) cumulative quantities: sums `cumsum()`, products `cumprod()`, maximum `cummax()`, minimum `cummin()`.


## Extracting and replacing data and index

* [index, time](https://zeileis.codeberg.page/zoo/man/index.html):
  Extract the index of a series.
* [index<-, time<-](https://zeileis.codeberg.page/zoo/man/index.html):
  Replace the index of a series.
* [coredata, coredata<-](https://zeileis.codeberg.page/zoo/man/coredata.html):
  Extract and replace the data associated with a `"zoo"` object.
* [lag](https://zeileis.codeberg.page/zoo/man/lag.zoo.html):
  Lagged observations.
* [diff](https://zeileis.codeberg.page/zoo/man/lag.zoo.html):
  Arithmetic and geometric differences.
* [start, end](https://zeileis.codeberg.page/zoo/man/index.html):
  Querying start and end of a series.
* [window, window<-](https://zeileis.codeberg.page/zoo/man/window.zoo.html):
  Subsetting of `"zoo"` objects using their index.


## `NA` handling

* [na.omit](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Omit `NA`s.
* [na.contiguous](https://zeileis.codeberg.page/zoo/man/zoo.html):
  Compute longest sequence of non-`NA` observations.
* [na.fill](https://zeileis.codeberg.page/zoo/man/na.fill.html):
  Impute `NA`s by filling gaps with specific values.
* [na.locf](https://zeileis.codeberg.page/zoo/man/na.locf.html):
  Impute `NA`s by carrying forward the last observation.
* [na.approx, na.spline](https://zeileis.codeberg.page/zoo/man/na.approx.html):
  Impute `NA`s by interpolation.
* [na.trim](https://zeileis.codeberg.page/zoo/man/na.trim.html):
  Remove leading and/or trailing `NA`s.


## Rolling analytics

* [rollapply](https://zeileis.codeberg.page/zoo/man/rollapply.html):
  Apply a function to rolling margin of an array.
* [rollmean](https://zeileis.codeberg.page/zoo/man/rollmean.html):
  More efficient functions for computing the rolling mean, median and maximum are `rollmean()`, `rollmedian()` and `rollmax()`, respectively.


## Methods for regular series

* [is.regular](https://zeileis.codeberg.page/zoo/man/is.regular.html):
  Checks whether a series is weakly (or strictly if `strict = TRUE`) regular.
* [frequency, deltat](https://zeileis.codeberg.page/zoo/man/frequency.html):
  Extracts the frequency or its reciprocal value respectively from a series, for `"zoo"` series the functions try to determine the regularity and frequency in a data-driven way.
* [cycle](https://zeileis.codeberg.page/zoo/man/zooreg.html):
  Gives the position in the cycle of a regular series.


## Time classes for monthly and quarterly data

* [yearmon](https://zeileis.codeberg.page/zoo/man/yearmon.html):
  Time index class for monthly data.
* [yearqtr](https://zeileis.codeberg.page/zoo/man/yearqtr.html):
  Time index class for quarterly data.