Count occurrences per entry in dataframe - r

Question

I have the following kind of dataframe (this is simplified example):
id = c("1", "1", "1", "2", "3", "3", "4", "4")
bank = c("a", "b", "c", "b", "b", "c", "a", "c")
df = data.frame(id, bank)
df
id bank
1 1 a
2 1 b
3 1 c
4 2 b
5 3 b
6 3 c
7 4 a
8 4 c
In this dataframe you can see that for some ids there are multiple banks, i.e. for id==1, bank=c(a,b,c).
The information I would like to extract from this dataframe is the overlap between id's within different banks and the count.
So for example for bank a: bank a has two persons (unique ids): 1 and 4. For these persons, I want to know what other banks they have
For person 1: bank b and c
For person 4: bank c
the total amount of other banks: 3, for which, b = 1, and c = 2.
So I want to create as output a sort of overlap table as below:
bank overlap amount
a b 1
a c 2
b a 1
b c 2
c a 2
c b 2

Answer 1

Took me a while to get a result, so I post it. Not as sexy as Ronak Shahs but same result.
id = c("1", "1", "1", "2", "3", "3", "4", "4")
bank = c("a", "b", "c", "b", "b", "c", "a", "c")
df = data.frame(id, bank)
df$bank <- as.character(df$bank)
resultlist <- list()
dflist <- split(df, df$id)
for(i in 1:length(dflist)) {
if(nrow(dflist[[i]]) < 2) {
resultlist[[i]] <- data.frame(matrix(nrow = 0, ncol = 2))
} else {
resultlist[[i]] <- as.data.frame(t(combn(dflist[[i]]$bank, 2)))
}
}
result <- setNames(data.table(rbindlist(resultlist)), c("bank", "overlap"))
result %>%
group_by(bank, overlap) %>%
summarise(amount = n())
bank overlap amount
<fct> <fct> <int>
1 a b 1
2 a c 2
3 b c 2

Answer 2

We may use data.table:
df = data.frame(id = c("1", "1", "1", "2", "3", "3", "4", "4"),
bank = c("a", "b", "c", "b", "b", "c", "a", "c"))
library(data.table)
setDT(df)[, .(bank = rep(bank, (.N-1L):0L),
overlap = bank[(sequence((.N-1L):1L) + rep(1:(.N-1L), (.N-1L):1))]),
by=id][,
.N, by=.(bank, overlap)]
#> bank overlap N
#> 1: a b 1
#> 2: a c 2
#> 3: b c 2
#> 4: <NA> b 1
Created on 2019-07-01 by the reprex package (v0.3.0)
Please note that you have b for id==2 which is not overlapping with other values. If you don't want that in the final product, just apply na.omit() on the output.

Answer 3

An option would be full_join
library(dplyr)
full_join(df, df, by = "id") %>%
filter(bank.x != bank.y) %>%
dplyr::count(bank.x, bank.y) %>%
select(bank = bank.x, overlap = bank.y, amount = n)
# A tibble: 6 x 3
# bank overlap amount
# <fct> <fct> <int>
#1 a b 1
#2 a c 2
#3 b a 1
#4 b c 2
#5 c a 2
#6 c b 2

Answer 4

Do you need to cover both banks in both the directions? Since a -> b is same as b -> a in this case here. We can use combn and create combinations of unique bank taken 2 at a time, find out length of common id found in the combination.
as.data.frame(t(combn(unique(df$bank), 2, function(x)
c(x, with(df, length(intersect(id[bank == x[1]], id[bank == x[2]])))))))
# V1 V2 V3
#1 a b 1
#2 a c 2
#3 b c 2
data
id = c("1", "1", "1", "2", "3", "3", "4", "4")
bank = c("a", "b", "c", "b", "b", "c", "a", "c")
df = data.frame(id, bank, stringsAsFactors = FALSE)