library(dplyr)

test <- data.frame('prod_id'= c("shoe", "shoe", "shoe", "shoe", "shoe",
"shoe", "boat", "boat","boat","boat","boat","boat", "ship", "ship",
 "ship",
"ship", "ship", "ship"),
       'seller_id'= c("a", "b", "c", "d", "e", "f", "a","g", "h", "r",
"q", "b", "qe", "dj", "d3", "kk", "dn", "de"),
       'Dich'= c(1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0),
       'price' = c(12, 200, 10, 4, 3, 4, 99, 55, 86, 88, 75, 64, 82,
 21, 44, 34, 22, 33)
        )

test2 <- test%>%
         group_by(prod_id) %>%
         (filter = price < 50)