R 在数据框中有条件地将增长率应用于给定的初始值

你可以用group_by和cumprod做到这一点.cumprod(growth+1)将对增长率进行组合；我用lag将第一年的增长率设置为0(以使其与基线相同).

dat |> 
  group_by(product, region) |> 
  mutate(sales_projected = sales[1] * cumprod(lag(growth, default = 0)+1))

# A tibble: 13 × 7
# Groups:   product, region [2]
   product  region   year growth sales sales_expected sales_projected
   <chr>    <chr>   <int>  <dbl> <int>          <int>           <dbl>
 1 productA regionA  2023   0.1    100            100            100 
 2 productA regionA  2024   0.1     NA            110            110 
 3 productA regionA  2025   0.1     NA            121            121 
 4 productA regionA  2026   0.1     NA            133            133.
 5 productA regionA  2027   0.1     NA            146            146.
 6 productA regionA  2028   0.1     NA            161            161.
 7 productA regionA  2029   0.1     NA            177            177.
 8 productA regionA  2030   0.1     NA            195            195.
 9 productA regionA  2031   0.1     NA            214            214.
10 productA regionA  2032   0.1     NA            236            236.
11 productA regionB  2023   0.06   100            100            100 
12 productA regionB  2024   0.06    NA            106            106 
13 productA regionB  2025   0.06    NA            112            112.

如果你想使用accumulate个函数，我认为你需要像这样使用accumulate2():

dat |> 
  group_by(product, region) |> 
  mutate(sales_expected = accumulate2(sales, growth[-1], \(x,y,g) x*(1+g)))

# A tibble: 13 × 7
# Groups:   product, region [2]
   product  region   year growth sales sales_expected sales_projected
   <chr>    <chr>   <int>  <dbl> <int>          <int>           <dbl>
 1 productA regionA  2023   0.1    100            100            100 
 2 productA regionA  2024   0.1     NA            110            110 
 3 productA regionA  2025   0.1     NA            121            121 
 4 productA regionA  2026   0.1     NA            133            133.
 5 productA regionA  2027   0.1     NA            146            146.
 6 productA regionA  2028   0.1     NA            161            161.
 7 productA regionA  2029   0.1     NA            177            177.
 8 productA regionA  2030   0.1     NA            195            195.
 9 productA regionA  2031   0.1     NA            214            214.
10 productA regionA  2032   0.1     NA            236            236.
11 productA regionB  2023   0.06   100            100            100 
12 productA regionB  2024   0.06    NA            106            106 
13 productA regionB  2025   0.06    NA            112            112.