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DT[
  id %in% 200:300,
  .(reg.val = sum(value)),
  by=region
][
  reg.val > 0,
  range(reg.val)
]

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## Serialization Does Not Trigger Promises

fx <- ff(stop('boom'))
fxa <- ff(stop('boom'))
fy <- ff(stop('boom boom'))

identical(serialize(fx, NULL), serialize(fxa, NULL))
## [1] TRUE
identical(serialize(fx, NULL), serialize(fy, NULL))
## [1] FALSE

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library(inline)
frow <- cfunction(sig=c(x='list'), body='
  R_xlen_t J = XLENGTH(x);
  R_xlen_t n = XLENGTH(VECTOR_ELT(x, 0));
  SEXP out = PROTECT(allocVector(INTSXP, n));
  int *outp = INTEGER(out);
  for (int j=0; j<J; j++) {
    int *col = INTEGER(VECTOR_ELT(x, j));
    for (int i=0; i<n; i++) {
      if(j) {outp[i] += col[i];} else {outp[i] = col[i];}

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mk_name <- function(name=NULL) {
  v <- as.character(packageVersion('rayrender'))
  dir <- file.path('~', 'Downloads', 'rr-tests')
  if(is.null(name)) {
    name <- sprintf( 'a_%s.png', format(Sys.time(), "%Y-%m-%d_%H%M%S"))
  } else {
    name <- sprintf('%s.png', name)
  }
  file.path(dir, v, name)
}

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# Because there is no way to tell data.table 
# "interpret this variable as a column name", it's possible to come up
# with corner cases.  I'll grant these are unlikely to occur in day
# to day use, but any function that uses `data.table` must account for
# them

# Low odds, and yes, there are workarounds, but this is
# what I mean by you have to think carefully to avoid 
# corner cases

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## GPL-2

## Tweet 1
## From https://github.com/djnavarro/ohno

add_with <- function(z) function(x, y) x + y + z
add_with(10)(1, 2)            # works
butcher <- function(x, y, f) {
  env <- new.env() # create a new environment
  environment(f) <- env

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# Compute Device Size To Fully Fill With Plot
#
# This is not tested extensively and I know very little about messing with
# grid.
#
# GPL-2
#
# @param gtable e.g. as produced by `ggplotGrob(ggplot() ...)`
# @param din device dimension in inches, ideally use defaults to avoid
#   calculation issues with npc units.

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# started with `foghorn`, but that comes with dependencies and
# slows down R startup.  `browseURL` just barely slows startup, 
# even if actual page is slow to load.

check_cran_old <- function(email) {
  utils::browseURL(
    sprintf(
      "https://cran.r-project.org/web/checks/check_results_%s.html",
      gsub("[^A-Za-z0-9_:.-]", "_", sub("@", "_at_", email))
) ) }

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# PNG to HTML

Code adapted from [@gdagstn](https://gist.github.com/gdagstn/1917e0e6f7dc91a8dde7cb789326c3bb).

```{r, echo=FALSE, comment="", results="asis"}
old.hooks <- fansi::set_knit_hooks(knitr::knit_hooks)
```

```{r echo=FALSE}
library(crayon)

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## Tests based on https://mailund.dk/posts/scoping-rules-and-nse/
# rm(list=ls())
if(length(ls())) message("you have variables defined in the environment")

library(wrapr)
lm_prop2a <- function(x, y, d, prop, eval) {
    let(c(x = x, y = y, prop = prop, d=d),
        summary(lm(y ~ x, data = d))$prop,
        eval = eval, envir=parent.frame())
}