nass_param: Get all possible values of a parameter
In usdarnass: USDA NASS Quick Stats API

Description Usage Arguments Value Examples

All possible values of a parameter for a given query. Helps to understand the columns of data.frame from nass_data.

nass_param(param = NULL, source_desc = NULL, sector_desc = NULL,
  group_desc = NULL, commodity_desc = NULL, short_desc = NULL,
  domain_desc = NULL, domaincat_desc = NULL, agg_level_desc = NULL,
  statisticcat_desc = NULL, state_name = NULL, asd_desc = NULL,
  county_name = NULL, region_desc = NULL, zip_5 = NULL,
  watershed_desc = NULL, year = NULL, freq_desc = NULL,
  reference_period_desc = NULL, token = NULL)

`param`	A valid parameter value. Available names are: source_desc, sector_desc, group_desc, commodity_desc, short_desc, domain_desc, domaincat_desc, agg_level_desc, statisticcat_desc, state_name, asd_desc, county_name, region_desc, zip_5, watershed_desc, year, freq_desc, and reference_period_desc.
`source_desc`	"Program" - Source of data ("CENSUS" or "SURVEY"). Census program includes the Census of Ag as well as follow up projects. Survey program includes national, state, and county surveys.
`sector_desc`	"Sector" - Five high level, broad categories useful to narrow down choices. ("ANIMALS & PRODUCTS", "CROPS", "DEMOGRAPHICS", "ECONOMICS", or "ENVIRONMENTAL")
`group_desc`	"Group" - Subsets within sector (e.g., under sector_desc = "CROPS", the groups are "FIELD CROPS", "FRUIT & TREE NUTS", "HORTICULTURE", and "VEGETABLES").
`commodity_desc`	"Commodity" - The primary subject of interest (e.g., "CORN", "CATTLE", "LABOR", "TRACTORS", "OPERATORS").
`short_desc`	"Data Item" - A concatenation of six columns: commodity_desc, class_desc, prodn_practice_desc, util_practice_desc, statisticcat_desc, and unit_desc.
`domain_desc`	"Domain" - Generally another characteristic of operations that produce a particular commodity (e.g., "ECONOMIC CLASS", "AREA OPERATED", "NAICS CLASSIFICATION", "SALES"). For chemical usage data, the domain describes the type of chemical applied to the commodity. The domain_desc = "TOTAL" will have no further breakouts; i.e., the data value pertains completely to the short_desc.
`domaincat_desc`	"Domain Category" - Categories or partitions within a domain (e.g., under domain_desc = "SALES", domain categories include $1,000 TO $9,999, $10,000 TO $19,999, etc).
`agg_level_desc`	"Geographic Level" - Aggregation level or geographic granularity of the data. ("AGRICULTURAL DISTRICT", "COUNTY", "INTERNATIONAL", "NATIONAL", "REGION : MULTI-STATE", "REGION : SUB-STATE", "STATE", "WATERSHED", or "ZIP CODE")
`statisticcat_desc`	"Category" - The aspect of a commodity being measured (e.g., "AREA HARVESTED", "PRICE RECEIVED", "INVENTORY", "SALES").
`state_name`	"State" - State full name.
`asd_desc`	"Ag District" - Ag statistics district name.
`county_name`	"County" - County name.
`region_desc`	"Region" - NASS defined geographic entities not readily defined by other standard geographic levels. A region can be a less than a state (SUB-STATE) or a group of states (MULTI-STATE), and may be specific to a commodity.
`zip_5`	"Zip Code" - US Postal Service 5-digit zip code.
`watershed_desc`	"Watershed" - Name assigned to the HUC.
`year`	"Year" - The numeric year of the data and can be either a character or numeric vector. Conditional values are also possible, for example a character vector of ">=1999" of "1999<=" will give years greater than or equal to 1999. Right now the logical values can either be greater/less than or equal to with the logical at either the beginning or end of a string with the year.
`freq_desc`	"Period Type" - Length of time covered ("ANNUAL", "SEASON", "MONTHLY", "WEEKLY", "POINT IN TIME"). "MONTHLY" often covers more than one month. "POINT IN TIME" is as of a particular day.
`reference_period_desc`	"Period" - The specific time frame, within a freq_desc.
`token`	API key, default is to use the value stored in `.Renviron` which is stored from the `nass_set_key` function. If there is no API key stored in the environment, a character string can be provided.

Character vector of all possible parameter values.

## Not run: 
# Return the program sources for data
nass_param("source_desc")

## End(Not run)

## Not run: 
# Return the group categories available in the CROPS sector
nass_param("group_desc", sector_desc = "CROPS")

## End(Not run)