Example

perc_wide

## # A tibble: 1 × 6
##   `2018_A` `2018_B` `2019_A` `2019_B` `2020_A` `2020_B`
##      <dbl>    <dbl>    <dbl>    <dbl>    <dbl>    <dbl>
## 1      100        0        0      100       40       60

perc_tidy <- perc_wide |> 
  pivot_longer(
    cols = everything(),
    names_to = c("year", "type"),
    names_sep = "_",
    values_to = "percentage"
  )
perc_tidy

## # A tibble: 6 × 3
##   year  type  percentage
##   <chr> <chr>      <dbl>
## 1 2018  A            100
## 2 2018  B              0
## 3 2019  A              0
## 4 2019  B            100
## 5 2020  A             40
## 6 2020  B             60

perc_tidy |> 
  pivot_wider(
    names_from = c(year, type),
    names_sep = "_",
    values_from = percentage
  )

## # A tibble: 1 × 6
##   `2018_A` `2018_B` `2019_A` `2019_B` `2020_A` `2020_B`
##      <dbl>    <dbl>    <dbl>    <dbl>    <dbl>    <dbl>
## 1      100        0        0      100       40       60