voronoiTreemap {WeightedTreemaps}

voronoiTreemap

Description

Create nested additively weighted Voronoi treemaps.

Usage

voronoiTreemap(
  data,
  levels,
  fun = sum,
  sort = TRUE,
  filter = 0,
  cell_size = NULL,
  custom_color = NULL,
  shape = "rectangle",
  maxIteration = 100,
  error_tol = 0.01,
  seed = NULL,
  positioning = "regular",
  verbose = FALSE,
  debug = FALSE
)

Arguments

data

(data.frame) A data.frame with one column for each hierarchical level

levels

(character) Character vector indicating the column names to be used. The order of names must correspond to the hierarchical levels, going from broad to fine

fun

(function) Function to be used to aggregate cell sizes of parental cells

sort

(logical) Should the columns of the data.frame be sorted before treemap generation?

filter

(numeric) Filter the supplied data frame to remove very small cells that may not be visible. The default is to remove cells with a relative target area below a threshold of zero (no negative values allowed). Computation time can increase when many small cells are present. For example, a threshold of 0.01 filters out all observations/cells below 1 % of the total area.

cell_size

(character) The name of the column used to control cell size. Can be one of levels or any other column with numerical data. NA or values equal or less than zero are not allowed as the cell area needs to be positive. The values in this column are aggregated by the function specified by fun. If cell_size = NULL, cell area is simply computed by the number of members for the respective cell (corresponding to rows in the data.frame).

custom_color

(character) An optional column that can be specified to control cell color. Cell colors are determined when drawing the treemap using drawTreemap, but the default is to use one of levels or cell size. Any other data source that shall be used instead has to be included in the treemap generation and explicitly specified here. The default value is NULL.

shape

(list or character) Set the initial shape of the treemap. Currently supported are the keywords "rectangle", "rounded_rect", "circle" or "hexagon". Alternatively the user can supply a named list with coordinates for a custom polygon. The slots of the list must be labeled 'x' and 'y'. The coordinates are not tested for validity, use on your own risk.

maxIteration

(numeric) Force algorithm to stop at this number of iterations for each parent cell. The algorithm usually converges to an acceptable solution fairly quickly, so it seems reasonable to restrict this number in order to save computation time. However, more iterations give higher accuracy.

error_tol

(numeric) The allowed maximum error tolerance of a cell. The algorithm will stop when all cells have lower error than this value. It is calculated as the absolute difference of a cell's area to its target area. The default is 0.01 (or 1 %) of the total parental area. Note: this is is different from a relative per-cell error, where 1 % would be more strict.

seed

(integer) The default seed is NULL, which will lead to a new random sampling of cell coordinates for each tesselation. If you want a reproducible arrangement of cells, set seed to an arbitrary number.

positioning

(character) Algorithm for positioning of starting coordinates of child cells in the parental cell using spsample(); "random" for completely random positions, "regular" for cells aligned to a grid sorted from bottom to top by name, "clustered" with regular positions of cells but sorted by name from inside out. Two variants "regular_by_area" and "clustered_by_area" will work as their counterparts but will sort by cell target area instead of cell name. positioning can be a single character or a vector of length(levels) to allow different positioning algorithms for each level.

verbose

(logical) If verbose is TRUE (default is FALSE), messages with statistics for each iteration of a treemap as well as a success message are printed to the console.

debug

(logical) If debug is TRUE (default is FALSE), the solution for each iteration is drawn to the viewport to allow some visual inspection. The weights, target area, and difference are printed to the console. It is not recommended to set this option to TRUE unless you know what you are doing, as it makes treemap generation much slower.

Details

This is a recursive wrapper function, making use of the original implementation of the voronoi tesselation from Paul Murrell, University of Auckland. The original functions were obtained and slightly modified from https://www.stat.auckland.ac.nz/~paul/Reports/VoronoiTreemap/voronoiTreeMap.html This function returns a treemap object instead of a plot. In order to actually draw the treemap, use drawTreemap.

Value

'voronoiTreemap' returns an object of the formal class 'voronoiResult'. It is essentially a list of objects related to the graphical representation of the treemap (polygons, labels, cell data) as well as data from the call of the function. It contains the following slots:

cells

'list' of polygons for drawing a treemap

data

'data.frame', the original data that was supplied to calling 'voronoiTreemap'

call

'list' of arguments used to call 'voronoiTreemap'

See Also

drawTreemap for drawing the treemap.

Examples

# load package
library(WeightedTreemaps)

# generate dummy data
df <- data.frame(
  A = rep(c("abcd", "efgh"), each = 4),
  B = letters[1:8],
  size = c(37, 52, 58, 27, 49, 44, 34, 45)
)

# compute treemap
tm <- voronoiTreemap(
  data = df,
  levels = c("B"),
  cell_size = "size",
  shape = "circle",
  positioning = "regular",
  seed = 123
)

# plot treemap with each cell colored by name (default)
drawTreemap(tm, label_size = 1, color_type = "categorical")

# plot treemap with each cell colored by name, but larger cells
# lighter and smaller cells darker
drawTreemap(tm, label_size = 1, color_type = "both")

# plot treemap with different color palette and style
drawTreemap(tm, label_size = 1, label_color = grey(0.3),
            border_color = grey(0.3), color_palette = heat.colors(6)
)