Manually specify the number of legend categories in tmap, including unrepresented categories-CodePudding

I am trying to specify a simple legend for a map of polygons and an integer variable, in which not all values within the range are present. I need this in order to have the same legend, with the same color scale, on comparable maps which differ in both the range and the particular values present. For example, the maximum value of a variable is 8 on any of the maps. I want the legend to show the values 0 to 8 even when 6, or any particular value, is not present for any polygon, and I want the labels on the legend to be 0 to 8, inclusive, with no pooling.

A replicable example:

library(tmap)
library(dplyr)
library(sf)
set.seed(1234)

shape <- st_read(system.file("shape/nc.shp", package ="sf")) %>% 
  st_transform(shape, crs = 4326)
shape$myvar <- as.integer(sample(x=c(c(base::rep(c(0,1,2,3,4),16),base::rep(5,15),c(7,7,7,7,8)))))

table(shape$myvar)

0  1  2  3  4  5  7  8 
16 16 16 16 16 15  4  1

I have tried many variations, but can't in this case get nine categories, with the corresponding labels.

mymap <- tm_shape(shape)  
  tm_fill(col = "myvar",
          style = "cat",
          breaks = c(0,1,2,3,4,5,6,7,8),
          n=9)
mymap

This legend is missing value 6.

In contrast, using the style = 'fixed' option like this:

mymap <- tm_shape(shape)  
  tm_fill(col = "myvar",
          style = "fixed",
          breaks = c(0,1,2,3,4,5,6,7,8),
          n=9)
mymap

The legend here has a category for the value '6', but pools the last two categories.

I tried putting an additional argument into tm_fill:

 style.args = classIntervals(var=shape$myvar,n=9)

This didn't change the output from the previous map.

Try as I might, I can't get all 9 categories.

Could someone please give me some suggestions as to how to get the simple legend I want, without having to use GIMP? Thanks in advance.

CodePudding user response：

Please find below one possible solution using tmap:

Reprex

Your data

library(tmap)
library(dplyr)
library(sf)

set.seed(1234)

shape <- st_read(system.file("shape/nc.shp", package ="sf")) %>% 
  st_transform(shape, crs = 4326)
shape$myvar <- as.integer(sample(x=c(c(base::rep(c(0,1,2,3,4),16),base::rep(5,15),c(7,7,7,7,8)))))

Suggested code

mymap <- tm_shape(shape)  
  tm_fill(col = "myvar",
          style = "fixed",
          breaks = c(0,1,2,3,4,5,6,7,8, Inf), 
          labels = c("0","1","2","3","4","5","6","7","8"))  
  tm_layout(inner.margins = c(0.02, 0.08, 0.02, 0.02))

mymap

^{Created on 2022-03-04 by the reprex package (v2.0.1)}