Create a new grob table.

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.

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
#> TableGrob (1 x 3) "layout": 0 grobs
gtable_show_layout(a)

# Add a grob:
rect <- rectGrob(gp = gpar(fill = "black"))
a <- gtable_add_grob(a, rect, 1, 1)
a
#> TableGrob (1 x 3) "layout": 1 grobs
#>   z     cells   name               grob
#> 1 1 (1-1,1-1) layout rect[GRID.rect.25]
plot(a)

# gtables behave like matrices:
dim(a)
#> [1] 1 3
t(a)
#> TableGrob (3 x 1) "layout": 1 grobs
#>   z     cells   name               grob
#> 1 1 (1-1,1-1) layout rect[GRID.rect.25]
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, ]
#> TableGrob (1 x 3) "layout": 0 grobs
b[, 1]
#> TableGrob (3 x 1) "layout": 0 grobs
b[2, 2]
#> TableGrob (1 x 1) "layout": 1 grobs
#>   z     cells   name               grob
#> 1 1 (1-1,1-1) layout rect[GRID.rect.25]

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