gtable {gtable} | R Documentation |
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.
gtable(widths = list(), heights = list(), respect = FALSE, name = "layout", rownames = NULL, colnames = NULL, vp = NULL)
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 |
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 |
vp |
a grid viewport object (or NULL). |
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.
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 accross
many cells.
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
.
gtable_row
, gtable_col
and
gtable_matrix
for convenient ways of
creating gtables.
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)