Reading and Writing zoo Series

read.zoo and write.zoo are convenience functions for reading and writing "zoo" series from/to text files. They are convenience interfaces to read.table and write.table, respectively. To employ read.csv, read.csv2, read.delim, read.delim2 instead of read.table additional functions read.csv.zoo etc. are provided.

Usage

read.zoo(file, format = "", tz = "", FUN = NULL,
  regular = FALSE, index.column = 1, drop = TRUE, FUN2 = NULL,
  split = NULL, aggregate = FALSE, ..., text, read = read.table)
  
write.zoo(x, file = "", index.name = "Index", row.names = FALSE, col.names = NULL,
  FUN = format, ...)

read.csv.zoo(..., read = read.csv)
read.csv2.zoo(..., read = read.csv2)
read.delim.zoo(..., read = read.delim)
read.delim2.zoo(..., read = read.delim2)

Arguments

file: character string or strings giving the name of the file(s) which the data are to be read from/written to. See read.table and write.table for more information. Alternatively, in read.zoo, file can be a connection or a data.frame (e.g., resulting from a previous read.table call) that is subsequently processed to a "zoo" series.
format: date format argument passed to FUN.
tz: time zone argument passed to as.POSIXct.
FUN: a function for processing the time index. In read.zoo this is the function that computes the index from the index.column, see the details. In write.zoo it is a function that formats the index prior to writing it to file.
regular: logical. Should the series be coerced to class "zooreg" (if the series is regular)?
index.column: numeric vector or list. The column names or numbers of the data frame in which the index/time is stored. If the read.table argument colClasses is used and "NULL" is among its components then index.column refers to the column numbers after the columns corresponding to "NULL" in colClasses have been removed. If specified as a list then one argument will be passed to argument FUN per component so that, for example, index.column = list(1, 2) will cause FUN(x[,1], x[,2], ...) to be called whereas index.column = list(1:2) will cause FUN(x[,1:2], ...) to be called where x is a data frame of characters data. Here ... refers to format and/or tz, if they specified as arguments. index.column = 0 can be used to specify that the row names be used as the index. In the case that no row names were input sequential numbering is used. If index.column is specified as an ordinary vector then if it has the same length as the number of arguments of FUN (or FUN2 in the event that FUN2 is specified and FUN is not) then index.column is converted to a list. Also it is always converted to a list if it has length 1.
drop: logical. If the data frame contains just a single data column, should the second dimension be dropped?
x: a "zoo" object.
index.name: character with name of the index column in the written data file.
row.names: logical. Should row names be written? Default is FALSE because the row names are just character representations of the index.
col.names: logical. Should column names be written? Default is to write column names only if x has column names.
FUN2: function. It is applied to the time index after FUN and before aggregate. If FUN is not specified but FUN2 is specified then only FUN2 is applied.
split: NULL or column number or name or vector of numbers or names. If not NULL then the data is assumed to be in long format and is split according to the indicated columns. See the R reshape command for description of long data. If split = Inf then the first of each run among the times are made into a separate series, the second of each run and so on. If split= -Inf then the last of each run is made into a separate series, the second last and so on.
aggregate: logical or function. If set to TRUE, then aggregate.zoo is applied to the zoo object created to compute the mean of all values with the same time index. Alternatively, aggregate can be set to any other function that should be used for aggregation. If FALSE (the default), no aggregation is performed and a warning is given if there are any duplicated time indexes. Note that most zoo functions do not accept objects with duplicate time indexes. See aggregate.zoo.
...: further arguments passed to other functions. In the read.*.zoo the arguments are passed to the function specified in read (unless file is a data.frame already). In write.zoo the arguments are passed to write.table.
text: character. If file is not supplied and this is, then data are read from the value of text via a text connection. See below for an example.
read: function. The function for reading file (unless it is a data.frame already).

Details

read.zoo is a convenience function which should make it easier to read data from a text file and turn it into a "zoo" series immediately. read.zoo reads the data file via read.table(file, ...). The column index.column (by default the first) of the resulting data is interpreted to be the index/time, the remaining columns the corresponding data. (If the file only has only column then that is assumed to be the data column and 1, 2, ... are used for the index.) To assign the appropriate class to the index, FUN can be specified and is applied to the first column.

To process the index, read.zoo calls FUN with the index as the first argument. If FUN is not specified, the following default is employed:

(a) If file is a data frame with a single index column that appears to be a time index already, then FUN = identity is used. The conditions for a readily produced time index are: It is not character or factor (and the arguments tz and format must not be specified).

(b) If the conditions from (a) do not hold then the following strategy is used. If there are multiple index columns they are pasted together with a space between each. Using the (pasted) index column: (1) If tz is specified then the index column is converted to POSIXct. (2) If format is specified then the index column is converted to Date. (3) Otherwise, a heuristic attempts to decide between "numeric", "POSIXct", and "Date" by trying them in that order (which may not always succeed though). By default, only the standard date/time format is used. Hence, supplying format and/or tz is necessary if some date/time format is used that is not the default. And even if the default format is appropriate for the index, explicitly supplying FUN or at least format and/or tz typically leads to more reliable results than the heuristic.

If regular is set to TRUE and the resulting series has an underlying regularity, it is coerced to a "zooreg" series.

To employ other functions than read.table to read the initial data, further convenience interfaces read.csv.zoo etc. are provided.

write.zoo is a convenience function for writing "zoo" series to text files. It first coerces its argument to a "data.frame", adds a column with the index and then calls write.table.

See also vignette("zoo-read", package = "zoo") for detailed examples.

Value

read.zoo returns an object of class "zoo" (or "zooreg").

Note

read.zoo works by first reading the data in using read.table and then processing it. This implies that if the index field is entirely numeric the default is to pass it to FUN or the built-in date conversion routine a number, rather than a character string. Thus, a date field such as 09122007 intended to represent September 12, 2007 would be seen as 9122007 and interpreted as the 91st day thereby generating an error.

This comment also applies to trailing decimals so that if 2000.10 were intended to represent the 10th month of 2000 in fact it would receive 2000.1 and regard it as the first month of 2000 unless similar precautions were taken.

In the above cases the index field should be specified to be "character" so that leading or trailing zeros are not dropped. This can be done by specifying a "character" index column in the "colClasses" argument, which is passed to read.table, as shown in the examples below.