R: Reading Excel tables from a workbook

readTable {XLConnect}

R Documentation

Reading Excel tables from a workbook

Description

Reads Excel tables (Office 2007+) from a workbook.

Usage

## S4 method for signature 'workbook,numeric'
readTable(object, sheet, table, header, rownames, colTypes, forceConversion, 
dateTimeFormat, check.names, useCachedValues, keep, drop, simplify, readStrategy)
## S4 method for signature 'workbook,character'
readTable(object, sheet, table, header, rownames, colTypes, forceConversion, 
dateTimeFormat, check.names, useCachedValues, keep, drop, simplify, readStrategy)

Arguments

`object`	The `workbook` to use
`sheet`	The index or name of the worksheet on which to look for the specified `table`
`table`	The name of the table 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.
`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.
`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.
`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)

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 1900-01-01. Fractional days represent hours, minutes, and seconds.

Author(s)

Martin Studer
Mirai Solutions GmbH https://mirai-solutions.ch

References

Overview of Excel tables
https://support.microsoft.com/en-us/office/overview-of-excel-tables-7ab0bb7d-3a9e-4b56-a3c9-6c94334e492c?ocmsassetid=ha010048546&correlationid=ecf0d51a-596f-42e5-9c05-8653648bb180&ui=en-us&rs=en-us&ad=us

Examples

## Not run: 
# mtcars xlsx file from demoFiles subfolder of package XLConnect
demoExcelFile <- system.file("demoFiles/mtcars.xlsx", package = "XLConnect")

# Load workbook
wb <- loadWorkbook(demoExcelFile)

# Read table 'MtcarsTable' from sheet 'mtcars_table'
data <- readTable(wb, sheet = "mtcars_table", table = "MtcarsTable")

## End(Not run)

[Package XLConnect version 1.0.10 Index]