readNamedRegion

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Reading named regions from a workbook

Reads named regions from a '>workbook.

Keywords
methods, IO
Usage
# S4 method for workbook
readNamedRegion(object, name, header, rownames, colTypes, forceConversion, 
dateTimeFormat, check.names, useCachedValues, keep, drop, simplify, readStrategy)
Arguments
object

The '>workbook to use

name

The name of the named region to read

header

The argument header specifies if the first row should be interpreted as column names. The default value is TRUE.

rownames

Index (numeric) or name (character) of column that should be used as row names. The corresponding column will be removed from the data set. Defaults to NULL which means that no row names are applied. Row names must be either integer or character. Non-numeric columns will be coerced to character.

colTypes

Column types to use when reading in the data. Specified as a character vector of the corresponding type names (see XLC; XLC$DATA_TYPE.<?>). You may also use R class names such as numeric, character, logical and POSIXt. The types are applied in the given order to the columns - elements are recycled if necessary. Defaults to character(0) meaning that column types are determined automatically (see the Note section for more information). By default, type conversions are only applied if the specified column type is a more generic type (e.g. from Numeric to String) - otherwise NA is returned. The forceConversion flag can be set to force conversion into less generic types where possible.

forceConversion

logical specifying if conversions to less generic types should be forced. Defaults to FALSE meaning that if a column is specified to be of a certain type via the colTypes argument and a more generic type is detected in the column, then NA will be returned (example: column is specified to be DateTime but a more generic String is found). Specifying forceConversion = TRUE will try to enforce a conversion - if it succeeds the corresponding (converted) value will be returned, otherwise NA. See the Note section for some additional information.

dateTimeFormat

Date/time format used when doing date/time conversions. Defaults to getOption("XLConnect.dateTimeFormat"). This should be a POSIX format specifier according to strptime although not all specifications have been implemented yet - the most important ones however are available.

check.names

logical specifying if column names of the resulting data.frame should be checked to ensure that they are syntactically valid valid variable names and are not duplicated. See the check.names argument of data.frame. Defaults to TRUE.

useCachedValues

logical specifying whether to read cached formula results from the workbook instead of re-evaluating them. This is particularly helpful in cases for reading data produced by Excel features not supported in XLConnect like references to external workbooks. Defaults to FALSE, which means that formulas will be evaluated by XLConnect.

keep

List of column names or indices to be kept in the output data frame. It is possible to specify either keep or drop, but not both at the same time. Defaults to NULL. If a vector is passed as argument, it will be wrapped into a list. This list gets replicated to match the length of the other arguments. Example: if name = c("NamedRegion1", "NamedRegion2", "NamedRegion3") and keep = c(1,2), keep will be internally converted into list(c(1,2)) and then replicated to match the number of named regions, i.e. keep = list(c(1,2), c(1,2), c(1,2)). The result is that the first two columns of each named region are kept. If keep = list(1,2) is specified, it will be replicated as list(1,2,1), i.e. respectively the first, second and first column of the named regions "NamedRegion1", "NamedRegion2", "NamedRegion3" will be kept.

drop

List of column names or indices to be dropped in the output data frame. It is possible to specify either keep or drop, but not both at the same time. Defaults to NULL. If a vector is passed as argument, it will be wrapped into a list. This list gets replicated to match the length of the other arguments. Example: if name = c("NamedRegion1", "NamedRegion2", "NamedRegion3") and drop = c(1,2), drop will be internally converted into list(c(1,2)) and then replicated to match the number of named regions, i.e. drop = list(c(1,2), c(1,2), c(1,2)). The result is that the first two columns of each named region are dropped. If drop = list(1,2) is specified, it will be replicated as list(1,2,1), i.e. respectively the first, second and first column of the named regions "NamedRegion1", "NamedRegion2", "NamedRegion3" will be dropped.

simplify

logical specifying if the result should be simplified, e.g. in case the data.frame would only have one row or one column (and data types match). Simplifying here is identical to calling unlist on the otherwise resulting data.frame (using use.names = FALSE). The default is FALSE.

readStrategy

character specifying the reading strategy to use. Currently supported strategies are:

  • "default" (default): Can handle all supported data types incl. date/time values and can deal directly with missing value identifiers (see setMissingValue)

  • "fast": Increased read performance. Date/time values are read as numeric (number of days since 1900-01-01; fractional days represent hours, minutes, and seconds) and only blank cells are recognized as missing (missing value identifiers as set in setMissingValue are ignored)

Details

The arguments name and header are vectorized. As such, multiple named regions can be read with one method call. If only one single named region is read, the return value is a data.frame.If multiple named regions are specified, the return value is a (named) list of data.frame's returned in the order they have been specified with the argument name.

Note

If no specific column types (see argument colTypes) are specified, readNamedRegion tries to determine the resulting column types based on the read cell types. If different cell types are found in a specific column, the most general of those is used and mapped to the corresponding R data type. The order of data types from least to most general is Boolean (logical) < DateTime (POSIXct) < Numeric (numeric) < String (character). E.g. if a column is read that contains cells of type Boolean, Numeric and String then the resulting column in R would be character since character is the most general type. Some additional information with respect to forcing data type conversion using forceConversion = TRUE:

  • Forcing conversion from String to Boolean: TRUE is returned if and only if the target string is "true" (ignoring any capitalization). Any other string will return FALSE.

  • Forcing conversion from Numeric to DateTime: since Excel understands Dates/Times as Numerics with some additional formatting, a conversion from a Numeric to a DateTime is actually possible. Numerics in this case represent the number of days since 1900-01-00 (yes, day 00! - see http://www.cpearson.com/excel/datetime.htm). Note that in R 0 is represented as 1899-12-31 since there is no 1900-01-00. Fractional days represent hours, minutes, and seconds.

References

What are named regions/ranges? http://www.officearticles.com/excel/named_ranges_in_microsoft_excel.htm How to create named regions/ranges? http://www.youtube.com/watch?v=iAE9a0uRtpM

See Also

'>workbook, readWorksheet, writeNamedRegion, writeWorksheet, readNamedRegionFromFile, readTable, onErrorCell

Aliases
  • readNamedRegion
  • readNamedRegion-methods
  • readNamedRegion,workbook-method
Examples
# NOT RUN {
## Example 1:
# mtcars xlsx file from demoFiles subfolder of package XLConnect
demoExcelFile <- system.file("demoFiles/mtcars.xlsx", package = "XLConnect")

# Load workbook
wb <- loadWorkbook(demoExcelFile)

# Read named region 'mtcars' (with default header = TRUE)
data <- readNamedRegion(wb, name = "mtcars")

## Example 2;
# conversion xlsx file from demoFiles subfolder of package XLConnect
excelFile <- system.file("demoFiles/conversion.xlsx", package = "XLConnect")

# Load workbook
wb <- loadWorkbook(excelFile)

# Read named region 'conversion' with pre-specified column types
# Note: in the worksheet all data was entered as strings!
# forceConversion = TRUE is used to force conversion from String
# into the less generic data types Numeric, DateTime & Boolean
df <- readNamedRegion(wb, name = "conversion", header = TRUE,
                      colTypes = c(XLC$DATA_TYPE.NUMERIC,
                                   XLC$DATA_TYPE.DATETIME,
                                   XLC$DATA_TYPE.BOOLEAN),
                      forceConversion = TRUE,
                      dateTimeFormat = "%Y-%m-%d %H:%M:%S")
                      
## Example 3:
# mtcars xlsx file from demoFiles subfolder of package XLConnect
demoExcelFile <- system.file("demoFiles/mtcars.xlsx", package = "XLConnect")

# Load workbook
wb <- loadWorkbook(demoExcelFile)

# Read the columns 1, 3 and 5 of the named region 'mtcars' (with default header = TRUE)
data <- readNamedRegion(wb, name = "mtcars", keep=c(1,3,5))
# }
Documentation reproduced from package XLConnect, version 0.2-15, License: GPL-3

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