How do we store a name and id function in For Loop in R

I am trying to create a for loop that iterates over one variable (customer_id) and stores a second variable (cust_nm) for writing the file name to excel and included the cust_nm in the file name.

library(tidyverse)
library(janitor)

df.1 <- tribble(
~customer_id, ~cust_nm  ,~period, ~cost1, ~cost2 ,
'cust1', 'pizzaco', '202201', 5, 10,
'cust2', 'sodaco','202202', 5, 10,
'cust1', 'pizzaco', '202203', 5, 10,
'cust2', 'sodaco', '202204', 5, 10,
)

cust_list <- df.1 %>% 
  select(customer_id,cust_nm) %>% 
  unique()


for (i in 1:length(cust_list)) {
test <- df.1 %>% filter(customer_id == cust_list[i][,1]) %>% 
  group_by(customer_id, cust_nm, period) %>% 
  summarise(cost1 = sum(cost1, na.rm = T),
            cost2 = sum(cost2, na.rm = T),
            total = cost1 + cost2) %>% 
  adorn_totals(where = 'row') 

writexl::write_xlsx(test, paste0("test_",cust_list[i][,2],".xlsx"))
}

The output expected would be 2 files with appropriate data labeled "test_pizzaco.xlsx" and "test_sodaco.xlsx"

I also tried seq_along because I understand that should allow to store the index and name, but was not able to create a working solution with that either.

Your advice is appreciated.

You could use purrr::map2() for this instead of a for-loop.

  library(tidyverse)
  library(janitor)
  
df.1 <- tribble(
  ~customer_id, ~cust_nm  ,~period, ~cost1, ~cost2 ,
  'cust1', 'pizzaco', '202201', 5, 10,
  'cust2', 'sodaco','202202', 5, 10,
  'cust1', 'pizzaco', '202203', 5, 10,
  'cust2', 'sodaco', '202204', 5, 10,
)

cust_list <- 
  df.1 %>% 
  select(customer_id,cust_nm) %>% 
  unique()

map2(cust_list$customer_id,
     cust_list$cust_nm,
     \(x, y) {
       out <- df.1 |>
         filter(customer_id == x) |>
         group_by(customer_id, cust_nm, period) |>
         summarise(
           cost1 = sum(cost1, na.rm = T),
           cost2 = sum(cost2, na.rm = T),
           total = cost1 + cost2,
           .groups = "keep"
         ) |>
         adorn_totals(where = 'row')
       
       writexl::write_xlsx(out, paste0("test_", y , ".xlsx"))
       
       out
     })
#> [[1]]
#>  customer_id cust_nm period cost1 cost2 total
#>        cust1 pizzaco 202201     5    10    15
#>        cust1 pizzaco 202203     5    10    15
#>        Total       -      -    10    20    30
#> 
#> [[2]]
#>  customer_id cust_nm period cost1 cost2 total
#>        cust2  sodaco 202202     5    10    15
#>        cust2  sodaco 202204     5    10    15
#>        Total       -      -    10    20    30

First, length(cust_list) is going to iterate over the number of columns, not the number of rows as I expect you're meaning to do. In this case it is the same number, but it's a convenience in this example that likely doesn't hold true very often. Instead, use for (i in 1:nrow(cust_list)).

Second, I suggest you simplify your cust_list[][] nomenclature to just reference the values you need.

For example, in your code, when i <- 1:

df.1 %>%
  filter(customer_id == cust_list[i][,1])
# Error in filter(., customer_id == cust_list[i][, 1]) : 
#   ℹ In argument: `customer_id == cust_list[i][, 1]`.
# Caused by error:
# ! `..1` must be of size 4 or 1, not size 2.

but this works:

df.1 %>%
  filter(customer_id == cust_list$customer_id[i])
# # A tibble: 2 × 5
#   customer_id cust_nm period cost1 cost2
#   <chr>       <chr>   <chr>  <dbl> <dbl>
# 1 cust1       pizzaco 202201     5    10
# 2 cust1       pizzaco 202203     5    10

(Similarly for the paste0.)

I think your full code should be:

for (i in 1:nrow(cust_list)) {
test <- df.1 %>% filter(customer_id == cust_list$customer_id[i]) %>% 
  group_by(customer_id, cust_nm, period) %>% 
  summarise(cost1 = sum(cost1, na.rm = T),
            cost2 = sum(cost2, na.rm = T),
            total = cost1 + cost2) %>% 
  adorn_totals(where = 'row') 

writexl::write_xlsx(test, paste0("test_",cust_list$cust_nm[i],".xlsx"))
}