squarebrackets Options

This help page explains the various global options that can be set for the 'squarebrackets' package, and how it affects the functionality.

Check Duplicates

The sb_x/sb2_x methods are the only methods where providing duplicate indices actually make sense.
For the other methods, it doesn't make sense.
Giving duplicate indices usually won't break anything; however, when replacing/transforming or removing subsets, it is almost certainly not the intention to provide duplicate indices.
Providing duplicate indices anyway might lead to unexpected results.
Therefore, for the methods where giving duplicate indices does not make sense, the chkdup argument is present.
This argument controls whether the method in question checks for duplicates (TRUE) or not (FALSE).

Setting chkdup = TRUE means the method in question will check for duplicate indices, and give an error when it finds them.

Setting chkdup = FALSE will disable these checks, which saves time and computation power, and is thus more efficient.

Since checking for duplicates can be expensive, it is set to FALSE by default.
The default can be changed in the squarebrackets.chkdup option.

Sticky

The slice_x, slice_wo, and slicev_x methods can already handle names (through the use.names argument), attributes specific to the mutable_atomic class, and attributes specific to the factor class.

Attributes which are not names, and not specific to mutable_atomic class, and not specific to the factor class - henceforth referred to as "other attributes" - are treated differently.
How the slice_x, slice_wo, and slicev_x methods handle these "other" attributes, is determined by the sticky option and argument.

When sticky = FALSE, the slice_x, slice_wo, and slicev_x methods will drop all other attributes.

By setting sticky = TRUE, all these other attributes, except comment and tsp, will be preserved;
The key advantage for this, is that classes that use static attributes (i.e. classes that use attributes that do not change when sub-setting), are automatically supported if sticky = TRUE, and no separate methods have to written for the slice_x, slice_wo, and slicev_x methods.
Attributes specific to classes like difftime, Date, POSIXct, roman, hexmode, octmode, and more, use static attributes.

Instead of setting sticky = TRUE or sticky = FALSE, one can also specify all classes that use static attributes that you'll be using in the current R session.
In fact, when 'squarebrackets' is loaded, the squarebrackets.sticky option is set as follows:

squarebrackets.sticky = c(
   "difftime", "Date", "POSIXct", "roman", "hexmode", "octmode"
)

So in the above default setting, sticky = TRUE for
"difftime", "Date", "POSIXct", "roman", "hexmode", "octmode".
Also in the above default setting, sticky = FALSE for other classes.

The reason the slice_x, slice_wo, and slicev_x methods need the sticky option, is because of the following.
Unlike most sb_/sb2_ methods, the slice_x, slice_wo, and slicev_x methods are not wrappers around the [ and [<- operators.
Therefore, most [ - S3 methods for highly specialized classes are not readily available for the slice_x, slice_wo, and slicev_x methods.
Which in turn means important class-specific attributes are not automatically preserved.
The sticky option is a convenient way to support a large number of classes, without having to write specific methods for them.

For specialized classes that use attributes that do change when sub-setting, separate dispatches for the slice_x, slice_wo, and slicev_x methods need to be written.
Package authors are welcome to create method dispatches for their own classes for these methods.