# How to Calculate Jaccard Similarity in R

The Jaccard similarity index measures the similarity between two sets of data. It can range from 0 to 1. The higher the number, the more similar the two sets of data.

The Jaccard similarity index is calculated as:

Jaccard Similarity = (number of observations in both sets) / (number in either set)

Or, written in notation form:

J(A, B) = |A∩B| / |A∪B|

This tutorial explains how to calculate Jaccard Similarity for two sets of data in R.

### Example: Jaccard Similarity in R

Suppose we have the following two sets of data:

```a <- c(0, 1, 2, 5, 6, 8, 9)
b <- c(0, 2, 3, 4, 5, 7, 9)```

We can define the following function to calculate the Jaccard Similarity between the two sets:

```#define Jaccard Similarity function
jaccard <- function(a, b) {
intersection = length(intersect(a, b))
union = length(a) + length(b) - intersection
return (intersection/union)
}

#find Jaccard Similarity between the two sets
jaccard(a, b)

0.4```

The Jaccard Similarity between the two lists is 0.4.

Note that the function will return if the two sets don’t share any values:

```c <- c(0, 1, 2, 3, 4, 5)
d <- c(6, 7, 8, 9, 10)

jaccard(c, d)

 0```

And the function will return if the two sets are identical:

```e <- c(0, 1, 2, 3, 4, 5)
f <- c(0, 1, 2, 3, 4, 5)

jaccard(e, f)

 1```

The function also works for sets that contain strings:

```g <- c('cat', 'dog', 'hippo', 'monkey')
h <- c('monkey', 'rhino', 'ostrich', 'salmon')

jaccard(g, h)

0.142857```

You can also use this function to find the Jaccard distance between two sets, which is the dissimilarity between two sets and is calculated as 1 – Jaccard Similarity.

```a <- c(0, 1, 2, 5, 6, 8, 9)
b <- c(0, 2, 3, 4, 5, 7, 9)

#find Jaccard distance between sets a and b
1 - jaccard(a, b)

 0.6```