CODEWITHSUNDEEP
r
user3012926
user3012926

Reputation: 127

Count number of identical values between two vectors

a<-c(19,24,34,47,47,47)
b<-c(3,14,24,25,47,47)

I want to know how many values in a match those in b, however i'm running into issues - when there are duplicate numbers present in both vectors. My desired answer for the above example would be 3 - because 24,47,47 - are shared between the two vectors.

If I use intersect:

intersect(a,b)

[1] 24 47

The 2nd matching 47 is ignored.

If I use %in%:

length(which(a %in% b))
[1] 4

The extra 47 in a is also counted.

I realise that I can do:

length(which(b %in% a))
[1] 3

However, I may also have cases where there is an extra matching value in b instead of a and so %in% is also not useful. For example:

a<-c(19,24,34,7,47,47)
b<-c(3,14,24,47,47,47)
length(which(b %in% a))
[1] 4 (I want the answer to still be 3)

So, without rearranging which vector comes first in the %in% function, for each test - I cannot figure out how to do this. Can somebody show me how?

Upvotes: 1

Views: 1240

Answers (3)

ThomasIsCoding
ThomasIsCoding

Reputation: 101034

You can use table + stack like below

with(
    as.data.frame.matrix(table(stack(list(a = a, b = b)))),
    sum((p <- pmin(a, b))[p > 0])
)

which gives

[1] 3

where

> as.data.frame.matrix(table(stack(list(a = a, b = b))))
   a b
3  0 1
14 0 1
19 1 0
24 1 1
25 0 1
34 1 0
47 3 2

Upvotes: 0

Đỗ C&#244;ng
Đỗ C&#244;ng

Reputation: 1

Reference: https://datascience.stackexchange.com/questions/9317/how-to-get-common-values-between-two-multi-sets

I have a method to make it Example:

a <- c(19,24,34,47,47,47)

b <- c(3,14,24,25,47,47)

d <- intersect(unique(a), unique(b))

min(length(a[a %in% d]),length(b[b %in% d]))

Using the min method to find. Image: Image Display

Upvotes: 0

Aaron Montgomery
Aaron Montgomery

Reputation: 1387

How about:

sum(pmin(
  table(a[a %in% intersect(a, b)]),
  table(b[b %in% intersect(a, b)])
))

We make table()s of the chunks of a, b that are common to both, then we take the smallest numbers from those tables and add them up.

Upvotes: 2

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