dotsInPolys length mismatch using data downloaded via tidycensus - r

Question

Can you help figure out the best way to resolve the length mismatch error thrown by dotsInPolys? I think it is because there are NA's or NULLs or some funk in the polygon data that makes it too long. Here's code that reproduces the error. Ultimately, I want to plot multiple races using Leaflet, but I can't produce the lat/lon needed for the random dots at this point.
require(maptools)
require(tidycensus)
person.number.divider <- 1000
census_api_key("ENTER KEY HERE", install = TRUE)
racevars <- c(White = "B02001_002", #"P005003"
Black = "B02001_003", #Black or African American alone
Latinx = "B03001_003"
)
nj.county <- get_acs(geography = "county", #tract
year = 2015,
variables = racevars,
state = "NJ", #county = "Harris County",
geometry = TRUE,
summary_var = "B02001_001")
library(sf)
st_write(nj.county, "nj.county.shp", delete_layer = TRUE)
nj <- rgdal::readOGR(dsn = "nj.county.shp") %>%
spTransform(CRS("+proj=longlat +datum=WGS84"))
nj#data <- nj#data %>%
tidyr::separate(NAME,
sep =",",
into = c("county", "state")) %>%
dplyr::select(estimat,variabl, GEOID, county) %>%
spread(key = variabl, value = estimat) %>%
mutate(county = trimws(county))
black.dots <- dplyr::select(nj#data, Black) / person.number.divider #%>%
black.dots <- dotsInPolys(nj, as.integer(black.dots$Black), f="random")
# Error in dotsInPolys(nj, as.integer(black.dots$Black), f = "random") :
# different lengths
length(nj) # 63 This seems too many, because I believe NJ has 21 counties.
length(black.dots$Black) # 21
This post (Advice on troubleshooting dotsInPolys error (maptools)) came close to helping me, but I couldn't see how to apply it to my case.
I can change the length of the nj spatialpolygonsdataframe by removing NA's and counties with a black pop greater than 0, but then the map doesn't plot multiple counties (maybe there is something wrong with the census download?).

Answer 1

It looks like you might have gotten this figured out, but I wanted to share another approach that uses sf::st_sample() instead of maptools::dotsInPolys(). One advantage of this is that you don't need to convert the sf object you get from tidycensus to a sp object.
In the following example I split the census data by race into a list three sf objects then perform st_sample() on each element of the list (each race). Next, I recombine the sampled points into one sf object with a new race variable for each point. Finally, I use tmap to make a map, though you could use ggplot2 or leaflet to map as well.
library(tidyverse)
library(tidycensus)
library(sf)
library(tmap)
person.number.divider <- 1000
racevars <- c(White = "B02001_002", #"P005003"
Black = "B02001_003", #Black or African American alone
Latinx = "B03001_003"
)
# get acs data with geography in "tidy" form
nj.county <- get_acs(geography = "county", #tract
year = 2015,
variables = racevars,
state = "NJ", #county = "Harris County",
geometry = TRUE,
summary_var = "B02001_001"
)
# split by race
county.split <- nj.county %>%
split(.$variable)
# randomly sample points in polygons based on population
points.list <- map(county.split, ~ st_sample(., .$estimate / person.number.divider))
# combine points into sf collections and add race variable
points <- imap(points.list, ~ st_sf(tibble(race = rep(.y, length(.x))), geometry = .x)) %>%
reduce(rbind)
# map!
tm_shape(nj.county) +
tm_borders(col = "darkgray", lwd = 0.5) +
tm_shape(points) +
tm_dots(col = "race", size = 0.01, pal = "Set2")
I don't have enough rep to post the map image directly, but here it is.