Gh fill

R/gh_fill.R

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+gh_fill <- function(geohashes, precision) {
+  if (length(unique(nchar(geohashes))) > 1) {
+    stop("Input Geohashes must all have the same precision level.")
+  }
+  if (any(grepl("['ailoAILO]", geohashes))) {
+    stop("Invalid Geohash; Valid characters: [0123456789bcdefghjkmnpqrstuvwxyz](any case)")
+  }
+  new_levels <- precision - nchar(geohashes[1])
+  base32 <-
+    unlist(strsplit("0123456789bcdefghjkmnpqrstuvwxyz", split = ""))
+  grid <-
+    do.call(data.table::CJ, append(list(geohashes), replicate(new_levels, base32, FALSE)))
+  do.call(paste0, grid)
+}

expandgrid_vs_CJ.Rmd

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+---
+title: "Justification for data.table import"
+output: html_document
+date: "2023-06-30"
+---
+
+```{r Define both functions}
+library(data.table)
+library(microbenchmark)
+
+gh_fill_dt <- function(geohashes, precision) {
+  if (uniqueN(nchar(geohashes)) > 1) {
+    stop("Input Geohashes must all have the same precision level.")
+  }
+  if (sum(grepl("['ailo]", geohashes)) > 0) {
+    stop("Invalid Geohash; Valid characters: [0123456789bcdefghjkmnpqrstuvwxyz]")
+  }
+
+  new_levels <- precision - nchar(geohashes[1])
+
+  base32 <-
+    unlist(strsplit("0123456789bcdefghjkmnpqrstuvwxyz", split = ""))
+
+  grid <-
+    do.call(data.table::CJ, append(list(geohashes), replicate(new_levels, base32, FALSE)))
+
+  do.call(paste0, grid)
+
+}
+
+
+gh_fill_base <- function(geohashes, precision) {
+  if (uniqueN(nchar(geohashes)) > 1) {
+    stop("Input Geohashes must all have the same precision level.")
+  }
+  if (sum(grepl("['ailo]", geohashes)) > 0) {
+    stop("Invalid Geohash; Valid characters: [0123456789bcdefghjkmnpqrstuvwxyz]")
+  }
+
+  new_levels <- precision - nchar(geohashes[1])
+
+  base32 <-
+    unlist(strsplit("0123456789bcdefghjkmnpqrstuvwxyz", split = ""))
+
+  grid <-
+    do.call(expand.grid, append(list(geohashes), replicate(new_levels, base32, FALSE)))
+
+  do.call(paste0, grid)
+
+}
+```
+
+
+
+```{r create test vector}
+test_vector <- gh_fill_dt(c("9w", "9x"), 4L) # Length of 2048
+```
+
+```{r benchmark test}
+microbenchmark(gh_fill_dt(test_vector, 6L))
+microbenchmark(gh_fill_base(test_vector, 6L))
+
+
+```
+

man/gh_fill.Rd

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+\name{gh_fill}
+\alias{gh_fill}
+
+\title{
+  Fill geohash(s)
+}
+\description{
+  Fill geohash prefix with members
+}
+\usage{
+gh_fill(geohashes, precision)
+}
+\arguments{
+  \item{geohashes}{ Character vector of input geohashes. They must all be of same precision. }
+  \item{precision}{ Positive \code{integer} scalar controlling the 'zoom level' -- how many characters should be used in the output. }
+}
+\details{
+  Note that each increas of \code{precision} by 1 results in an output 32 times larger.
+}
+\value{
+  \code{character} vector of geohashes corresponding to the input.
+}
+\references{
+  \url{http://geohash.org/} ( Gustavo Niemeyer's original geohash service )
+}
+\author{
+  Garnet vanWeerden
+}
+
+\examples{
+# Single geohash input
+gh_fill("9w", 6L)
+
+# Vector of geohashes of same length. 
+gh_fill(c("9w", "9x", "9y"), 6L)
+}

tests/testthat/test-fill.R

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+test_that('gh_fill works', {
+
+  # Test single string
+  expect_equal(gh_fill("9w", 3L), c("9w0", "9w1", "9w2", "9w3", "9w4", "9w5",
+                                    "9w6", "9w7", "9w8", "9w9", "9wb", "9wc",
+                                    "9wd", "9we", "9wf", "9wg", "9wh", "9wj",
+                                    "9wk", "9wm", "9wn", "9wp", "9wq", "9wr",
+                                    "9ws", "9wt", "9wu", "9wv", "9ww", "9wx",
+                                    "9wy", "9wz"))
+  # Test vector of inputs
+  expect_equal(gh_fill(c("9w", "9x"), 3L),
+               c("9w0", "9w1", "9w2", "9w3", "9w4", "9w5",
+                 "9w6", "9w7", "9w8", "9w9", "9wb", "9wc",
+                 "9wd", "9we", "9wf", "9wg", "9wh", "9wj",
+                 "9wk", "9wm", "9wn", "9wp", "9wq", "9wr",
+                 "9ws", "9wt", "9wu", "9wv", "9ww", "9wx",
+                 "9wy", "9wz",
+                 "9x0", "9x1", "9x2", "9x3", "9x4", "9x5",
+                 "9x6", "9x7", "9x8", "9x9", "9xb", "9xc",
+                 "9xd", "9xe", "9xf", "9xg", "9xh", "9xj",
+                 "9xk", "9xm", "9xn", "9xp", "9xq", "9xr",
+                 "9xs", "9xt", "9xu", "9xv", "9xw", "9xx",
+                 "9xy", "9xz"))
+
+  # Going down level by level should have same result as doing it all at once
+  expect_equal(gh_fill("9w", 4L),
+               gh_fill(
+                 gh_fill("9w", 3L),
+                 4L)
+               )
+
+  # Only Valid Characters
+  expect_error(gh_fill("i9", 3L), 'Invalid Geohash; Valid characters: [0123456789bcdefghjkmnpqrstuvwxyz](any case)', fixed = TRUE)
+
+})