Allow requesting subsets of ZCTAs

[kmishra9]

Hey there,

One use case I'm using tidycensus for is to generate ~100 covariates for a model for data that gets refreshed decently often. For that reason, I'd like to avoid pulling all 100 covariates (which, as I'm sure you can imagine, can take a long time) for every zip code in the country, and instead would love to specify the necessary zip codes before the query, similar to how the state parameter is used when working at the state level.

library('tidycensus')
library('tidyverse')

monthly_housing_costs <- c(
    "MonthlyHousingCost_0_100"     = "B25104_002",
    "MonthlyHousingCost_100_199"   = "B25104_003",
    "MonthlyHousingCost_200_299"   = "B25104_004",
    "MonthlyHousingCost_300_399"   = "B25104_005",
    "MonthlyHousingCost_400_499"   = "B25104_006",
    "MonthlyHousingCost_500_599"   = "B25104_007",
    "MonthlyHousingCost_600_699"   = "B25104_008",
    "MonthlyHousingCost_700_799"   = "B25104_009",
    "MonthlyHousingCost_800_899"   = "B25104_010",
    "MonthlyHousingCost_900_999"   = "B25104_011",
    "MonthlyHousingCost_1000_1499" = "B25104_012",
    "MonthlyHousingCost_1500_1999" = "B25104_013",
    "MonthlyHousingCost_2000_2499" = "B25104_014",
    "MonthlyHousingCost_2500_2999" = "B25104_015",
    "MonthlyHousingCost_3000_plus" = "B25104_016",
    "MonthlyHousingCost_0"         = "B25104_017"
)

acs_2017_housing_costs_zcta_limited <- get_acs(
    geography = "zcta",
    variables = monthly_housing_costs,
    year = 2017,
    output = "wide",
    state = c('92867', '94608')
) %>% glimpse()
#> Getting data from the 2013-2017 5-year ACS
#> Error: ZCTAs can only be requested for the entire country, not within states or counties.

^{Created on 2020-08-28 by the reprex package (v0.3.0)}

[mfherman]

This could be implemented as the API accepts one or more ZCTAs as a parameter:

https://api.census.gov/data/2018/acs/acs5?get=B01003_001E&for=zip%20code%20tabulation%20area:11222,11211,10536

@walkerke, what do you think? I know you've shied away from adding too many arguments to get_acs() - just not sure how common it would be for a user to want a subset of ZCTAs.

[walkerke]

Good find @mfherman! I think this makes sense as a feature given that the API accommodates it. It wouldn't help for calls with geometry = TRUE as we still have to pull in the full ZCTA geometry then subset given how Census makes the data available, but for non-geometry calls it'd be nice to have.

[kmishra9]

Great! I'm glad its possible, in scope, and look forward to the day we can specify ZCTAs :)

Until then, I'll continue caching results locally (2 seconds vs 20 minutes)!

[walkerke]

I could see this as part of a broader discussion tied to #298, where users could specify geographical hierarchies that are not tied to the traditional state/county hierarchy that we tend to accommodate in the package. I'm sending up a new version to CRAN today but I'd like to keep this in mind for the next release.

[walkerke]

This is now implemented thanks to @mfherman!