# Playing with Roman numerals

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What is the longest year number (yet) written in Roman numerals ?

```library(tidyverse) tibble(y = 1:2020) %>% mutate(r = as.roman(y), l = str_length(r)) %>% slice_max(l)
# A tibble: 1 x 3 y r l
1 1888 MDCCCLXXXVIII 13```

It is year 1888, with 13 characters…

And the largest writable number being 3899, according to the strict rules in R (however some say it’s 3999),

```tibble(y = 1:5000) %>% mutate(r = as.roman(y), l = str_length(r)) %>% filter(lead(is.na(l))) %>% slice_min(l)
# A tibble: 1 x 3 y r l
1 3899 MMMDCCCXCIX 11```

the longest overall year will be year 3888 with 15 characters.

```tibble(y = 1:3899) %>% mutate(r = as.roman(y), l = str_length(r)) %>% slice_max(l)
# A tibble: 1 x 3 y r l
1 3888 MMMDCCCLXXXVIII 15```

Nice pattern :

`tibble(y = 1:3899) %>% mutate(r = as.roman(y), l = str_length(r)) %>% ggplot(aes(y, l)) + # geom_col(width = 1) + geom_point(alpha = .2) + # geom_line(alpha = .5) + geom_smooth() + labs(title = "Characters length of roman numeral years", x = "year", y = "characters")`

And there are only eleven palindromic years :

```tibble(y = 1:3899) %>% mutate(r = as.character(as.roman(y)), rr = stringi::stri_reverse(r)) %>% filter(r == rr, str_length(r) > 1)
# A tibble: 11 x 3 y r rr    1 2 II II 2 3 III III 3 19 XIX XIX 4 20 XX XX 5 30 XXX XXX 6 190 CXC CXC 7 200 CC CC 8 300 CCC CCC 9 1900 MCM MCM 10 2000 MM MM 11 3000 MMM MMM ```