Show NULL

Back to initial problem. We want NULL to be a valid R value for a glue():

show_null <- function(x, val = "NULL") {
  if (is.null(x)) {
    val
  } else {
    x
  }
}

glue_null <- transforming_glue(show_null)

# Example from Prologue
glue_null("I have {x} apples and {y} oranges.")
## I have 10 apples and NULL oranges.

Fixed width output

With {stringr} package you can force an output to be fixed width:

str_width <- function(x, width) {
  if (str_length(x) > width) {
    str_trunc(x, width, side = "right")
  } else {
    str_pad(x, width, side = "right")
  }
}

glue_width <- transforming_glue(partial(str_width, width = 10))

short_oh <- "Ooh!"
long_oh <- "Oooooooooooh!"
glue_width("This puzzles ({short_oh}) and surprises ({long_oh}) me.")
## This puzzles (Ooh!      ) and surprises (Ooooooo...) me.

Note usage of partial() here: it takes function along with its arguments’ values and modifies it by “pre-filling” those arguments.

Enclose output

In some situation you might want to explicitly show which strings represent R objects in the output. You can do that by enclosing the output in some sort of braces:

enclose <- function(x, start = "<", end = ">") {
  paste0(start, x, end)
}

glue_enclose <- transforming_glue(enclose)

glue_enclose("What if I had {x} oranges?")
## What if I had <10> oranges?

Bizarro encryption

One possibly useful pattern is to encrypt the used data to prevent it from seeing by untrustworthy eyes. Here we will use simplified bizarro() example from this insightful UseR 2018 talk by the amazing Jennifer (Jenny) Bryan. Here glue_bizarro() “reverts” R objects based on their type.

str_reverse <- function(x) {
  vapply(
    strsplit(x, ""),
    FUN = function(z) paste(rev(z), collapse = ""),
    FUN.VALUE = ""
  )
}

bizarro <- function(x) {
  cls <- class(x)[[1]]
  
  switch(
    cls,
    logical = !x,
    integer = -x,
    numeric = -x,
    character = str_reverse(x),
    x
  )
}

glue_bizarro <- transforming_glue(bizarro)

new_fruit <- "pomegranate"
glue_bizarro(
  "Then I might have {x + 10} apples. Is that {TRUE}?
   Maybe I want {new_fruit}?"
)
## Then I might have -20 apples. Is that FALSE?
## Maybe I want etanargemop?

Ultimate example

Using already familiar functional programming technique, we can create an ultimate glue() wrapper as a combination, or rather compose()-ition, of all previous examples. The most important part is supply them in correct order:

glue_ultimate <- transforming_glue(
  compose(
    enclose,
    partial(str_width, width = 10),
    # To ensure that input of `str_width()` is character
    as.character,
    show_null,
    bizarro
  )
)

glue_ultimate(
  "I have {x} apples and {y} oranges.
   This puzzles ({short_oh}) and surprises ({long_oh}) me.
   What if I had {x} oranges?
   Then I might have {x + 10} apples. Is that {TRUE}?
   Maybe I want {new_fruit}?"
)
## I have <-10       > apples and <NULL      > oranges.
## This puzzles (<!hoO      >) and surprises (<!hooooo...>) me.
## What if I had <-10       > oranges?
## Then I might have <-20       > apples. Is that <FALSE     >?
## Maybe I want <etanarg...>?

sessionInfo()
## R version 3.4.4 (2018-03-15)
## Platform: x86_64-pc-linux-gnu (64-bit)
## Running under: Ubuntu 16.04.5 LTS
## 
## Matrix products: default
## BLAS: /usr/lib/openblas-base/libblas.so.3
## LAPACK: /usr/lib/libopenblasp-r0.2.18.so
## 
## locale:
##  [1] LC_CTYPE=ru_UA.UTF-8       LC_NUMERIC=C              
##  [3] LC_TIME=ru_UA.UTF-8        LC_COLLATE=ru_UA.UTF-8    
##  [5] LC_MONETARY=ru_UA.UTF-8    LC_MESSAGES=ru_UA.UTF-8   
##  [7] LC_PAPER=ru_UA.UTF-8       LC_NAME=C                 
##  [9] LC_ADDRESS=C               LC_TELEPHONE=C            
## [11] LC_MEASUREMENT=ru_UA.UTF-8 LC_IDENTIFICATION=C       
## 
## attached base packages:
## [1] methods   stats     graphics  grDevices utils     datasets  base     
## 
## other attached packages:
## [1] stringr_1.3.1 purrr_0.2.5   glue_1.3.0   
## 
## loaded via a namespace (and not attached):
##  [1] Rcpp_0.12.18     bookdown_0.7     crayon_1.3.4     digest_0.6.15   
##  [5] rprojroot_1.3-2  backports_1.1.2  magrittr_1.5     evaluate_0.11   
##  [9] blogdown_0.8     rlang_0.2.1.9000 stringi_1.2.4    rmarkdown_1.10  
## [13] tools_3.4.4      xfun_0.3         yaml_2.2.0       compiler_3.4.4  
## [17] htmltools_0.3.6  knitr_1.20