R: gtable

gtable {gtable} | R Documentation

## gtable

### Description

gtable

A grob table captures all the information needed to layout grobs in a table structure. It supports row and column spanning, offers some tools to automatically figure out the correct dimensions, and makes it easy to align and combine multiple tables.

### Usage

    gtable(widths = list(), heights = list(), respect = FALSE,
      name = "layout", rownames = NULL, colnames = NULL, vp = NULL)

### Arguments

`widths` | a unit vector giving the width of each column
`heights` | a unit vector giving the height of each row
`respect` | a logical vector of length 1: should the aspect ratio of height and width specified in null units be respected. See `grid.layout` for more details
`name` | a string giving the name of the table. This is used to name the layout viewport
`rownames, colnames` | character vectors of row and column names, used for characteric subsetting, particularly for `gtable_align`, and `gtable_join`.
`vp` | a grid viewport object (or NULL).

### Details

Each grob is put in its own viewport - grobs in the same location are not combined into one cell. Each grob takes up the entire cell viewport so justification control is not available.

It constructs both the viewports and the gTree needed to display the table.

### Components

There are three basics components to a grob table: the specification of table (cell heights and widths), the layout (for each grob, its position, name and other settings), and global parameters.

It's easier to understand how `gtable` works if in your head you keep the table separate from it's contents. Each cell can have 0, 1, or many grobs inside. Each grob must belong to at least one cell, but can span across many cells.

### Layout

The layout details are stored in a data frame with one row for each grob, and columns:

- `t` top extent of grob

- `r` right extent of grob

- `b` bottom extent of

- `l` left extent of grob

- `z` the z-order of the grob - used to reorder the grobs before they are rendered

- `clip` a string, specifying how the grob should be clipped: either `"on"`, `"off"` or `"inherit"`

- `name`, a character vector used to name each grob and its viewport

You should not need to modify this data frame directly - instead use functions like `gtable_add_grob`.

### See Also

`gtable_row`, `gtable_col` and `gtable_matrix` for convenient ways of creating gtables.

### Examples

    library(grid)
    a <- gtable(unit(1:3, c("cm")), unit(5, "cm"))
    a
    gtable_show_layout(a)

    # Add a grob:
    rect <- rectGrob(gp = gpar(fill = "black"))
    a <- gtable_add_grob(a, rect, 1, 1)
    a
    plot(a)

    # gtables behave like matrices:
    dim(a)
    t(a)
    plot(t(a))

    # when subsetting, grobs are retained if their extents lie in the
    # rows/columns that retained.

    b <- gtable(unit(c(2, 2, 2), "cm"), unit(c(2, 2, 2), "cm"))
    b <- gtable_add_grob(b, rect, 2, 2)
    b[1, ]
    b[, 1]
    b[2, 2]

    # gtable have row and column names
    rownames(b) <- 1:3
    rownames(b)[2] <- 200
    colnames(b) <- letters[1:3]
    dimnames(b)

[Package gtable version 0.2.0 Index]