This function provides a high level API for writing a data.frame to
an Excel 2007 worksheet. It calls several low level functions in the
process. Its goal is to provide the conveniency of
write.csv by borrowing from its signature.
Internally, write.xlsx uses a double loop in over all the elements of
the data.frame so performance for very large data.frame may be
an issue. Please report if you experience slow performance. Dates and
POSIXct classes are formatted separately after the insertion. This also
adds to processing time.
If x is not a data.frame it will be converted to one.
Function write.xlsx2 uses addDataFrame which speeds up the
execution compared to write.xlsx by an order of magnitude for large
spreadsheets (with more than 100,000 cells).
The default formats for Date and DateTime columns can be changed via the two
package options xlsx.date.format and xlsx.datetime.format.
They need to be specified in Java date format
https://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html.
Writing of password protected workbooks is supported for Excel 2007 OOXML
format only. Note that in Linux, LibreOffice is not able to read password
protected spreadsheets.