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Create a legend placement specification

Source: R/legend.R
seq_legend.Rd

Constructs a SeqLegendSpec object that describes where and how a legend group should be rendered. The spec captures placement intent only — no rendering logic is executed here. It is consumed by the legend-rendering layer in a later batch.

Usage

seq_legend(
  keys,
  title = NULL,
  position = "inside",
  x = 0.5,
  y = 0.5,
  hjust = 0,
  orientation = NULL,
  nrow = NULL,
  ncol = NULL,
  side = NULL
)

Arguments

keys

A single LegendKey, or a named or unnamed list of LegendKey objects. Required.

title

Optional character string. The legend group title drawn above or beside the key block.

position

Character. One of "inside", "track_margin", or "canvas_margin". Controls which area the legend occupies. Default "inside".

x

Numeric in [0, 1]. Horizontal position of the legend anchor within the target area. Default 0.5.

y

Numeric in [0, 1]. Vertical position of the legend anchor within the target area. Default 0.5.

hjust

Numeric in [0, 1]. Horizontal justification of the legend content block relative to the anchor. 0 = left-aligned, 1 = right-aligned. Default 0.

orientation

Character. One of "horizontal" or "vertical". Controls whether keys are laid out as a row or a column. When NULL (default), orientation is inferred from side: "vertical" for side %in% c("left", "right"), "horizontal" otherwise.

nrow

Integer or NULL. Number of rows in the key grid. When both nrow and ncol are NULL, defaults to 1 row (all keys in one row for horizontal orientation) or 1 column (all keys in one column for vertical orientation).

ncol

Integer or NULL. Number of columns in the key grid.

side

Character or NULL. For position %in% c("track_margin", "canvas_margin"), which margin to target. One of "top", "bottom", "left", "right". When NULL, defaults to "top" for margin positions and is left NULL for "inside".

Value

A SeqLegendSpec S3 object (a named list with class "SeqLegendSpec").

Examples

k1 <- LegendKey(label = "H3K27ac", color = "firebrick")
k2 <- LegendKey(label = "H3K4me3", color = "steelblue")

# Inside the track, top-left
spec <- seq_legend(list(k1, k2), title = "Marks", x = 0.02, y = 0.95)

# In the outer track margin, bottom
spec <- seq_legend(list(k1, k2), position = "track_margin", side = "bottom")