更改图例标题会中断ggplot2中的图例颜色

Question

I'm trying to change the legend title on my ggplot. Here are two examples (partly from here ); the first one is with the sf package, which is what I'm really using. The second one is without that package which seems to have the same problem.

With sf , what I want:

cities <- tibble::tribble(
  ~ lon,    ~ lat,    ~ name,      ~ pop,
  5.121420, 52.09074, "Utrecht",   311367,
  6.566502, 53.21938, "Groningen", 189991,
  4.895168, 52.37022, "Amsterdam", 779808 
) %>% sf::st_as_sf(coords = c("lon", "lat"), crs = 4326)

lines_sfc <- sf::st_sfc(list(
  sf::st_linestring(rbind(cities$geometry[[1]], cities$geometry[[2]])),
  sf::st_linestring(rbind(cities$geometry[[2]], cities$geometry[[3]]))
))

lines <- sf::st_sf(
  id = 1:2,
  size = c(10,50),
  geometry = lines_sfc,
  crs = 4326
)

ggplot() + 
  geom_sf(aes(colour = pop, size=pop), data = cities)

which gives a nice legend with bad title:

Using this , I modified my script to change the legend:

ggplot() + 
  geom_sf(aes(colour = pop), data = cities) + 
  guides(colour=guide_legend(title="New color"))

which gives:

The legend isn't a gradient anymore, why?

If you don't have sf , the same happens with a geom_bar :

ggplot() + 
  geom_bar(aes(x=name, y=pop, colour = pop), stat="identity", data = cities)

gives:

while this :

ggplot() + 
  geom_bar(aes(x=name, y=pop, colour = pop), stat="identity", data = cities) + 
  guides(colour=guide_legend(title="New color"))

gives:

Is there a way to change only the title of the legend and not the whole thing?

my sessionInfo:

R version 3.4.3 (2017-11-30)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows Server >= 2012 x64 (build 9200)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] sp_1.2-6           rgeos_0.3-26       ggplot2_2.2.1.9000 dplyr_0.7.4        sf_0.6-1          

loaded via a namespace (and not attached):
 [1] Rcpp_0.12.14           pillar_1.0.1           compiler_3.4.3         git2r_0.19.0           plyr_1.8.4            
 [6] bindr_0.1              viridis_0.4.0          class_7.3-14           tools_3.4.3            digest_0.6.13         
[11] viridisLite_0.2.0      memoise_1.1.0          tibble_1.4.1           gtable_0.2.0           lattice_0.20-35       
[16] pkgconfig_2.0.1        rlang_0.1.6.9002       cli_1.0.0              DBI_0.7                rstudioapi_0.6        
[21] rgdal_1.2-16           curl_2.8.1             bindrcpp_0.2           gridExtra_2.3          e1071_1.6-8           
[26] withr_2.1.1.9000       httr_1.3.1             knitr_1.18             devtools_1.13.3        classInt_0.1-24       
[31] grid_3.4.3             glue_1.1.1             R6_2.2.2               udunits2_0.13          magrittr_1.5          
[36] scales_0.5.0.9000      RStudioShortKeys_0.1.0 units_0.5-1            assertthat_0.2.0       colorspace_1.3-2      
[41] labeling_0.3           utf8_1.1.3             lazyeval_0.2.1         munsell_0.4.3          crayon_1.3.4    

Answer 1

ggplot() + 
  geom_sf(aes(colour = pop, size=pop), data = cities) +
  scale_color_continuous(name = 'newname')

You can call the color scale and just specify the name