grid (version 3.3)

unit: Function to Create a Unit Object

Description

This function creates a unit object --- a vector of unit values. A unit value is typically just a single numeric value with an associated unit.

Usage

unit(x, units, data=NULL)

Arguments

x

A numeric vector.

units

A character vector specifying the units for the corresponding numeric values.

data

This argument is used to supply extra information for special unit types.

Value

• An object of class "unit".

WARNING

There is a special function unit.c for concatenating several unit objects.

The c function will not give the right answer.

There used to be "mylines", "mychar", "mystrwidth", "mystrheight" units. These will still be accepted, but work exactly the same as "lines", "char", "strwidth", "strheight".

Details

Unit objects allow the user to specify locations and dimensions in a large number of different coordinate systems. All drawing occurs relative to a viewport and the units specifies what coordinate system to use within that viewport.

Possible units (coordinate systems) are: [object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

A number of variations are also allowed for the most common units. For example, it is possible to use "in" or "inch" instead of "inches" and "centimetre" or "centimeter" instead of "cm".

A special units value of "null" is also allowed, but only makes sense when used in specifying widths of columns or heights of rows in grid layouts (see grid.layout).

The data argument must be a list when the unit.length() is greater than 1. For example, unit(rep(1, 3), c("npc", "strwidth", "inches"), data = list(NULL, "my string", NULL)).

It is possible to subset unit objects in the normal way and to perform subassignment (see the examples), but a special function unit.c is provided for combining unit objects.

Certain arithmetic and summary operations are defined for unit objects. In particular, it is possible to add and subtract unit objects (e.g., unit(1, "npc") - unit(1, "inches")), and to specify the minimum or maximum of a list of unit objects (e.g., min(unit(0.5, "npc"), unit(1, "inches"))).

See Also

unit.c

Examples

unit(1, "npc")
unit(1:3/4, "npc")
unit(1:3/4, "npc") + unit(1, "inches")
min(unit(0.5, "npc"), unit(1, "inches"))
unit.c(unit(0.5, "npc"), unit(2, "inches") + unit(1:3/4, "npc"),
       unit(1, "strwidth", "hi there"))
x <- unit(1:5, "npc")
x[2:4]
x[2:4] <- unit(1, "mm")
x