如何在 R 的数据框中找出逗号在一行中出现的最大数量？

Question

I want to find out the maximum amount comma had appeared in a row in a single column.

For example,

     Cars
1    Bugatti (4)","Ferrari (7)","Audi (10)
2    Toyota (6)
3    Tesla (9)","Mercedes(8)
4    Suzuki (11)","Mitsubishi (19)","Ford (7)","BMW (6)

For the table column above, the maximum number a comma had appeared in a row is 3, and it is on row 4. How do I achieve this on a much more larger data (4000+ rows)?

Answer 1

You can use gregexp() to return a vector of the positions of the comma(s) in each string. Then you can apply the length() function to count up the commas:

sapply(gregexpr(",", df$cars), length)
## 2 1 1 3

To answer the exact question asked, just wrap the above line of code in max() to determine the maximum number of times a comma appeared in one of your strings.

---

The above actually returns a "1" when a "0" is expected. There is probably a more elegant solution, but here's a function that will handle zeros correctly:

count_commas <- function(x) {
    y <- sapply(gregexpr(",", x), as.integer) # get position of commas
    y <- lapply(y, function(y) if(y[1] == -1) NULL else y) # replace zeros
    return( sapply(y, length) ) # return count of commas
}

count_commas(df$cars)
# 2 0 1 3

Answer 2

My idea is to remove the non-comma characters and calculate the number of chars.

I have no clue which class of object you are using for cars . Assuming your input is

cars <- c(' Bugatti (4)","Ferrari (7)","Audi (10)','Toyota (6)','Tesla (9)","Mercedes(8)','Suzuki (11)","Mitsubishi (19)","Ford (7)","BMW (6)')

then you can use nchar(gsub("[^,]","", cars)) to get the number of commas of each row.