How to append variables to shapefile in R?

Question

I want to create a map of China that demonstrates the value of the ethnic heterogeneity index. I want to generate the map as in this webpage, https://mgimond.github.io/Spatial/mapping-data-in-r.html

I gathered the .shp file of provinces from Hijmans, Robert J., University of California, Berkeley. Museum of Vertebrate Zoology. Second-level Administrative Divisions, China, 2015 [map]. No Scale Provided. Retrieved April 15, 2021, from https://geodata.lib.utexas.edu/catalog/stanford-nt024fn0432

But I do not know how to append "ethnic heterogeneity index" to this file? The ethnic heterogeneity index is stored as a CSV. file and the common variable for both files is "province". My current csv file does not contain the longitude and latitude information for provinces, is that the problem?

chinaprovincedf <- as(chinaprovince, "data.frame")
Error in as(chinaprovince, "data.frame") : 
  internal problem in as(): “sf” is(object, "data.frame") is TRUE, but the metadata asserts that the 'is' relation is FALSE

I am not sure how to proceed.

Answer 1

library(sf)
library(dplyr)

# this are the polygons
china = read_sf("https://geodata.lib.utexas.edu/download/file/stanford-nt024fn0432-geojson.json")

# make a dummy data.frame for the example
# in your case use read.csv for your file
# check we change the name here to illustrate the join
china_heterogeneity = data.frame(province = china$name_2, heterogeneity = runif(seq_along(china$name_2)) )

# you may see there's no geometry in this data frame
head(china_heterogeneity)
  province heterogeneity
1   Anqing     0.2678299
2   Bengbu     0.6505222
3   Bozhou     0.3048307
4   Chaohu     0.9352014
5  Chizhou     0.5902616
6  Chuzhou     0.0210071

# we use left join, in the "by" argument we pass the common variable, as named in # both data frames
left_join(china, china_heterogeneity, by = c("name_2" = "province")) %>%
  select(heterogeneity) %>% plot(graticule = T)