data split

firms <- paste0("Firm", sprintf("%03i", 1L:500L))
brands <- paste0("Brand", sprintf("%03i", 1L:100L))
brandsList <- replicate(length(firms), sample(brands, sample(1L:20L, 1L)))
brandsFirms <- unlist(mapply(function(x, y) c(x, y), firms, brandsList, USE.NAMES = FALSE))
head(brandsFirms, 24L)
#  [1] "Firm001"  "Brand046" "Brand024" "Brand021" "Brand050" "Brand011"
#  [7] "Brand078" "Brand003" "Brand061" "Brand016" "Brand085" "Brand057"
#  [13] "Firm002"  "Brand006" "Brand072" "Brand024" "Brand057" "Brand083"
#  [18] "Brand082" "Brand044" "Brand099" "Brand075" "Firm003"  "Brand058"

# 所以firms1是你的vector 1，brandsFirms是你的vector 2

loc <- match(firms, brandsFirms)
idx <- findInterval(seq_along(brandsFirms), loc)
idx_firms <- firms[idx]
idx_firms[loc] <- "firms"
output <- split(brandsFirms, idx_firms)
output$firms <- NULL
head(output, 3L)
# $Firm001
# [1] "Brand046" "Brand024" "Brand021" "Brand050" "Brand011" "Brand078"
# [7] "Brand003" "Brand061" "Brand016" "Brand085" "Brand057"
#
# $Firm002
# [1] "Brand006" "Brand072" "Brand024" "Brand057" "Brand083" "Brand082"
# [7] "Brand044" "Brand099" "Brand075"
#
# $Firm003
# [1] "Brand058" "Brand069" "Brand047"