Match numbers or first letter before a character - regex

Arthur Carvalho Brito

I am trying in R to match a specific pattern to make a separation into columns

Consider these examples of strings:

1-EXAMPLE
23-EXAMPLE2
A-EXAMPLE3
EXAMPLE-4

How can I write a regex to be used in tidyr::extract so that the separation happens as follows:

1   EXAMPLE
23  EXAMPLE2
A   EXAMPLE3
NA  EXAMPLE-4

I want to make a separation at the first - mark if before it there are only numbers, or if there is a single letter beforehand (as in the third case), but not if there more (as in example 4)

Thank you!

akrun

We can use case_when to insert a character before we do extract

library(dplyr)
library(stringr)
library(tidyr)
df1 %>% 
    mutate(col1 = case_when(str_detect(trimws(col1), '^([A-Z]|[0-9]+)\\s*-', 
       negate = TRUE) ~ str_c('-', col1), TRUE ~ trimws(col1))) %>% 
    extract(col1, into = c('col1', 'col2'), '^([A-Z]|\\d+)?\\s*-(.*)') %>% 
    mutate(col1 = na_if(col1, ''))

-output

col1      col2
1    1   EXAMPLE
2   23  EXAMPLE2
3    A  EXAMPLE3
4 <NA> EXAMPLE-4

data

df1 <- structure(list(col1 = c("1-EXAMPLE", "23-EXAMPLE2", "A-EXAMPLE3", 
"EXAMPLE-4")), class = "data.frame", row.names = c(NA, -4L))

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edited at2021-06-20

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