readNamedRegion: Reading named regions from a workbook

Description

Reads named regions from a workbook.

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)

Author

Martin Studer
Thomas Themel
Nicola Lambiase
Mirai Solutions GmbH https://mirai-solutions.ch

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.
When reading dates, if your system uses a time zone that has / had daylight saving time, certain dates / timestamps will not be read exactly as they were written. See https://poi.apache.org/apidocs/dev/org/apache/poi/ss/usermodel/DateUtil.html#getJavaDate-double-

References

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

Examples

Run this code

if (FALSE) {
## 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))
}

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