Planning for a trip to Cornwall, I was churning through some mysteries there, largely picking them at random from the map. I worked my way through this one by hand, copying the puzzle into a text editor and separating the pairs manually before finally transferring it into RStudio and plotting the result. I moved on.

Later, I twigged that this would be an ideal demonstration of several powerful aspects of string manipulation in R, so I returned and wrote a program to do the same.

The puzzle is straightforward: just plot the coordinate pairs and you should see the cache coordinates spelled out in your plot.

I chose to use a regular expression to extract the contents of each pair of parentheses, using the `str_extract_all` function from the `stringr` package. This “regex” approach is powerful but also makes for a daunting read. If you are new to regular expressions, this website can help you understand them a little better. There is also a cheatsheet section to help remind more experienced users. Regular expressions are definitely worth the trouble.

```library(tidyverse)
library(magrittr)
library(stringr)
B10 <- "(-3,-1)(-3,-5)(-2,-3)(-1,-5)(-1,-1) (-8,9)(-10,9)(-10,7)(-9,7)(-8,5)(-10,5) (-7,5)(-7,9)(-5,9)(-5,5)(-7,5) (-5,-6)(-6,-8)(-6,-10)(-4,-10)(-4,-8)(-6,-8) (2,9)(1,7)(1,5)(3,5)(3,7)(1,7) (5,-8)(3,-8)(3,-10)(5,-10)(5,-6)(4,-6)(4,-8) (2,-1)(0,-1)(0,-3)(1,-3)(2,-5)(0,-5) (2,-6)(0,-6)(0,-8)(1,-8)(2,-10)(0,-10) (-13,5)(-13,9)(-11,5)(-11,9) (12,7)(10,7)(10,5)(12,5)(12,9)(11,9)(11,7) (-1,-8)(-3,-8)(-3,-6)(-1,-6)(-1,-8)(-2,-10) (8,9)(7,7)(7,5)(9,5)(9,7)(7,7) (4,5)(4,9)(6,9)(6,5)(4,5) (-2,8)(-1,9)(-1,5)"

B10 %>%
str_extract_all("(?<=\\()([^\\(\\)]+)(?=\\))") %>%
unlist() %>%
paste(collapse=",") %>%
str_split(",") %>%
unlist() %>%
as.numeric() %>%
matrix(ncol = 2, byrow = TRUE) %>%
plot(type="l")```

I chose to collapse the pairs of numbers into one big vector and make them into a matrix, which I then plotted with a line plot. It’s not tidy because of the lines joining different characters, but it’s legible.

I just noticed that there are spaces in the original text, probably to separate individual characters. Therefore I could have made something even more sophisticated, separating by spaces first and producing a tidier plot. But I’ve solved this puzzle twice now; a third time just for perfection would be overkill.

The bulk of the work in this puzzle is preparing the data, which is similar to many data visualisation or analysis workflows. `stringr` is the main engine of my solution, plucking the pairs from the parentheses, and again splitting them by the separator in order to coerce messy character data into a clean set of numbers that can be plotted. And it’s scalable, unlike the by-hand method I first used. This task involved 156 numbers, but it could just as easily have been 1560, making the manual approach a poor use of solving time.

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1. Given the form of the data (maybe it was messier than shown, or had other elements?) the treatment of the parentheses seems a bit overkill: wouldn’t a simple str_extract_all(“(-?\\d+)”) do the same job?

(Warning in advance: the double backslashed escape I’ve used to indicate “digits” might collapse to a single backslash when showing on the website, as do all the escapes in your post above. Maybe they need 4 (count’em!) backslashes to render correctly?)

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1. Indeed, your solution is far better than mine, as it knocks out other steps along the way. The code becomes:
B10 %>%
str_extract_all(“(-?\\d+)”) %>%
unlist() %>%
as.numeric() %>%
matrix(ncol = 2, byrow = TRUE) %>%
plot(type=”l”)

Good work!

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2. jnorthrop2016 says:

Thanks for the post.
I attempted to run the code and received this error…
Error: ‘\(‘ is an unrecognized escape in character string starting “”(?<=\(".
I presume that the code needs a "\\" in place of each "\".

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1. Thanks for pointing that out. The backslashes should indeed by doubled up. I thought I pasted from my RStudio code so it should have been like that but something went wrong somewhere. I’ve updated the post to reflect that.

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