Add a color legend to a map (original) (raw)
Description
When a color palette function is used in a map (e.g.colorNumeric), a color legend can be automatically derived from the palette function. You can also manually specify the colors and labels for the legend.
Usage
addLegend(
map,
position = c("topright", "bottomright", "bottomleft", "topleft"),
pal,
values,
na.label = "NA",
bins = 7,
colors,
opacity = 0.5,
labels = NULL,
labFormat = labelFormat(),
title = NULL,
className = "info legend",
layerId = NULL,
group = NULL,
data = getMapData(map)
)
labelFormat(
prefix = "",
suffix = "",
between = " – ",
digits = 3,
big.mark = ",",
transform = identity
)
Arguments
| map | a map widget object created from leaflet() |
|---|---|
| position | the position of the legend |
| pal | the color palette function, generated fromcolorNumeric(), colorBin(), colorQuantile(), orcolorFactor() |
| values | the values used to generate colors from the palette function |
| na.label | the legend label for NAs in values |
| bins | an approximate number of tick-marks on the color gradient for thecolorNumeric palette if it is of length one; you can also provide a numeric vector as the pre-defined breaks (equally spaced) |
| colors | a vector of (HTML) colors to be used in the legend ifpal is not provided |
| opacity | the opacity of colors |
| labels | a vector of text labels in the legend corresponding tocolors |
| labFormat | a function to format the labels derived from pal andvalues (see Details below to know what labelFormat() returns by default; you can either use the helper function labelFormat(), or write your own function) |
| title | the legend title |
| className | extra CSS classes to append to the control, space separated |
| layerId | the ID of the legend; subsequent calls to addLegendor addControl with the same layerId will replace this legend. The ID can also be used with removeControl. |
| group | group name of a leaflet layer group. Supplying this value will tie the legend to the leaflet layer group with this name and will auto add/remove the legend as the group is added/removed, for example via layerControl. You will need to set the group when you add a layer (e.g. addPolygons) and supply the same name here. |
| data | the data object from which the argument values are derived; by default, it is the data object provided to leaflet()initially, but can be overridden |
| prefix | a prefix of legend labels |
| suffix | a suffix of legend labels |
| between | a separator between x[i] and x[i + 1] in legend labels (by default, it is a dash) |
| digits | the number of digits of numeric values in labels |
| big.mark | the thousand separator |
| transform | a function to transform the label value |
Details
The labFormat argument is a function that takes the argumenttype = c("numeric", "bin", "quantile", "factor"), plus, arguments for different types of color palettes. For the colorNumeric() palette,labFormat takes a single argument, which is the breaks of the numeric vector, and returns a character vector of the same length. ForcolorBin(), labFormat also takes a vector of breaks of lengthn but should return a character vector of length n - 1, with the i-th element representing the interval c(x[i], x[i + 1]). For colorQuantile, labFormat takes two arguments, the quantiles and the associated probabilities (each of length n), and should return a character vector of length n - 1 (similar to the colorBin()palette). For colorFactor(), labFormat takes one argument, the unique values of the factor, and should return a character vector of the same length.
By default, labFormat is basically format(scientific = FALSE, big.mark = ",") for the numeric palette, as.character() for the factor palette, and a function to return labels of the form ‘x[i] - x[i + 1]’ for bin and quantile palettes (in the case of quantile palettes,x is the probabilities instead of the values of breaks).
Examples
# !formatR
library(leaflet)
# a manual legend
leaflet() %>% addTiles() %>% addLegend(
position = "bottomright",
colors = rgb(t(col2rgb(palette())) / 255),
labels = palette(), opacity = 1,
title = "An Obvious Legend"
)
# an automatic legend derived from the color palette
df <- local({
n <- 300; x <- rnorm(n); y <- rnorm(n)
z <- sqrt(x ^ 2 + y ^ 2); z[sample(n, 10)] <- NA
data.frame(x, y, z)
})
pal <- colorNumeric("OrRd", df$z)
leaflet(df) %>%
addTiles() %>%
addCircleMarkers(~x, ~y, color = ~pal(z), group = "circles") %>%
addLegend(pal = pal, values = ~z, group = "circles", position = "bottomleft") %>%
addLayersControl(overlayGroups = c("circles"))
# format legend labels
df <- data.frame(x = rnorm(100), y = rexp(100, 2), z = runif(100))
pal <- colorBin("PuOr", df$z, bins = c(0, .1, .4, .9, 1))
leaflet(df) %>%
addTiles() %>%
addCircleMarkers(~x, ~y, color = ~pal(z), group = "circles") %>%
addLegend(pal = pal, values = ~z, group = "circles", position = "bottomleft") %>%
addLayersControl(overlayGroups = c("circles"))
leaflet(df) %>%
addTiles() %>%
addCircleMarkers(~x, ~y, color = ~pal(z), group = "circles") %>%
addLegend(pal = pal, values = ~z, labFormat = labelFormat(
prefix = "(", suffix = ")%", between = ", ",
transform = function(x) 100 * x
), group = "circles", position = "bottomleft" ) %>%
addLayersControl(overlayGroups = c("circles"))