如何计算不同长度的弦的频率

Question

I'm begining in R and it's a little bit hard for me sometimes. I have a big data frame of 100000 observations and in this data frame I have a column id and I need to compute the most frequent id in the column. But the problem is that there sometimes different id in a string separate by a '&'. I gonna keep an exemple it's easier:

id             value
1                1
1                2
2&3&4            6
2&5&7&8          1
2&4&5            3
2                3

So, I'm supposed to obtain 2
There can be until 20 '&' in a string.

Thanks in advance,

Answer 1

The data seems to be this:

df<-structure(list(id = structure(c(1L, 1L, 3L, 5L, 4L, 2L), .Label = c("1", 
"2", "2&3&4", "2&4&5", "2&5&7&8"), class = "factor"), value = c(1L, 
2L, 6L, 1L, 3L, 3L)), .Names = c("id", "value"), class = "data.frame", row.names = c(NA, 
-6L))

First step is to have a vector with all the ids :

unlist(strsplit(as.character(df[,1]),'&'))
# [1] "1" "1" "2" "3" "4" "2" "5" "7" "8" "2" "4" "5" "2"

then we get the frequencies:

table(unlist(strsplit(as.character(df[,1]),'&')))

# 1 2 3 4 5 7 8 
# 2 4 1 2 2 1 1 

and then we diplay the number with the highest frequency (the table is ordered in decreasing order):

names(sort(table(unlist(strsplit(as.character(df[,1]),'&'))),decreasing=T)[1])
# [1] "2"