It is easy to the draw a Venn diagram with the following code:

```
library(VennDiagram)

set.seed(1) # For reproducibility of results
xx.1 <- list(A = sample(LETTERS, 15), B = sample(LETTERS, 15), 
             C = sample(LETTERS, 15), D = sample(LETTERS, 15))

venn.diagram(xx.1, filename ="1.tiff", height = 1000, width = 1000)

```

![A venn diagram with four sets](https://i.imgur.com/IalHBjs.png)

But how do I figure out the items in each field? For example, I would like to know what are the two letters only found in A? 

**EDIT**:

Here is my solution, it is not perfect but could give all the intersections.

```
library(reshape)
library(R.utils)

## data
A <- data.frame(names = sample(LETTERS, 15), A = 1)
B <- data.frame(names = sample(LETTERS, 15), B = 1)
C <- data.frame(names = sample(LETTERS, 15), C = 1)
D <- data.frame(names = sample(LETTERS, 15), D = 1)

## a merged data frame.
xx.1 <- list(A = A, B= B, C= C, D = D)
xx.2 <- merge_recurse(xx.1)

## function
ff.vennFourItems <- function(X)
{
    ## get the items from venn diagram; for four sets, there are 15 fields;

    vennItems <- list()
    cate.n <- names(X)[2:5]

    for (i in 1:15)
    {
        xx.b <- intToBin(i)
        ## make it four bits;
        if (nchar(xx.b) != 4)
        {
            xx.b <- paste(paste(rep("0", 4 - nchar(xx.b)), collapse = ""), xx.b, sep ="") 
        }

        xx.b.1 <- unlist(strsplit(xx.b, ""))

        xx.1 <- X

        if(xx.b.1[1] == "0") { xx.1 <- xx.1[is.na(xx.1[, 2]), ] }
        else { xx.1 <-  xx.1[!is.na(xx.1[, 2]), ] }

        if(xx.b.1[2] == "0") { xx.1 <- xx.1[is.na(xx.1[, 3]), ] }
        else { xx.1 <-  xx.1[!is.na(xx.1[, 3]), ] }

        if(xx.b.1[3] == "0") { xx.1 <- xx.1[is.na(xx.1[, 4]), ] }
        else { xx.1 <-  xx.1[!is.na(xx.1[, 4]), ] }

        if(xx.b.1[4] == "0") { xx.1 <- xx.1[is.na(xx.1[, 5]), ] }
        else { xx.1 <-  xx.1[!is.na(xx.1[, 5]), ] }

        chipC <-  paste(paste(cate.n, collapse = "#"), xx.b, sep = "***")

        if (dim(xx.1)[1] == 0) 
        {
            xx.2 <- list(genes = dim(xx.1)[1], chipC = chipC, chipCN = i, detailChipS = xx.1, shortL = data.frame(genes = "noInteraction", cl = i, fullCl = chipC))
        }
        else
        {
            xx.2 <- list(genes = dim(xx.1)[1], chipC = chipC, chipCN = i, detailChipS = xx.1, shortL = data.frame(genes = as.character(xx.1[, 1]), cl = i, fullCl = chipC))
        }
        vennItems <- c(vennItems, list(xx.2))
    }

    vennItems
}

xx.3 <- ff.vennFourItems(xx.2)
str(xx.3)
List of 15
 $ :List of 5
  ..$ genes      : int 1
  ..$ chipC      : chr "A#B#C#D***0001"
  ..$ chipCN     : int 1
  ..$ detailChipS:'data.frame': 1 obs. of  5 variables:
  .. ..$ names: Factor w/ 25 levels "A","B","E","F",..: 25
  .. ..$ A    : num NA
  .. ..$ B    : num NA
  .. ..$ C    : num NA
  .. ..$ D    : num 1
  ..$ shortL     :'data.frame': 1 obs. of  3 variables:
  .. ..$ genes : Factor w/ 1 level "Z": 1
  .. ..$ cl    : int 1
  .. ..$ fullCl: Factor w/ 1 level "A#B#C#D***0001": 1
 $ :List of 5
  ..$ genes      : int 0
  ..$ chipC      : chr "A#B#C#D***0010"
  ..$ chipCN     : int 2

```