Using dplyr and stringr to replace all values starts with

We can do this using base R without converting to character class by assigning the levels with 'fruit' to 'fruit' and use aggregate to get the sum

levels(df$food)[grepl("fruit", levels(df$food))] <- "fruit"
aggregate(sold~food, df, sum)
#   food      sold
#1 bread  99.41637
#2 fruit 300.41033
#3  meat 100.84746

data

set.seed(24)
df <- data.frame(food = c("fruit banana", "fruit apple", "fruit grape", 
                 "bread", "meat"), sold = rnorm(5, 100))

It is working for me, I think your data is in factors:

Using stringsAsFactors=FALSE while making the data as below or you can run options(stringsAsFactors=FALSE) in the R environment to avoid the same:

df <- data.frame(food = c("fruit banana", "fruit apple", "fruit grape", "bread", "meat"), sold = rnorm(5, 100),stringsAsFactors = FALSE)

df %>%
mutate(food = replace(food, str_detect(food, "fruit"), "fruit")) %>% 
group_by(food) %>% 
summarise(sold = sum(sold))

Output:

 # A tibble: 3 × 2
       food      sold
      <chr>     <dbl>
    1 bread  99.67661
    2 fruit 300.28520
    3  meat  99.88566