Understanding Venn Diagrams in R and Adding Comma Separators

As a beginner in R, it’s not uncommon to come across various visualization tools like the triple Venn diagram. The question of how to add comma separators for big numbers is a common one, but it may require some digging into the underlying code.

Introduction to Venn Diagrams

A Venn diagram is a graphical representation used to show the relationship between sets. In this case, we’re dealing with three overlapping circles representing “Dogs”, “Cats”, and “Horses”. Each circle represents a set of elements, and the overlap areas represent the relationships between these sets.

The VennDiagram package in R is used to create Venn diagrams with various options for customization. In this example, we’re using draw.triple.venn to generate a triple Venn diagram with specific labels and formatting.

Understanding the Code

Let’s break down the code snippet provided:

library(VennDiagram)
grid.newpage()
draw.triple.venn(area1=49644, area2=38697, area3=33281, n12=14221, n23=11026,
                 n13=13635, n123=4242, category=c("DOGS", "CATS", "HORSES"), 
                 cex=1.6, cat.cex=1.8, lwd=2, fill=c("blue", "pink1", "grey50"))

This code initializes the VennDiagram package, creates a new grid page, and then uses draw.triple.venn to generate the Venn diagram with specific parameters.

Catching the Grob Object

The grob object is the graphical representation of the Venn diagram. To manipulate it, we need to catch it in an object using draw.triple.venn.

V <- draw.triple.venn(...)  ## catch it in an object

Exploring the Grob Object

Using str(V), we can explore the structure of the grob object.

str(V)
# [...]
# $ :List of 11
# ..$ label        : chr "26030"                <-- here "label"
# ..$ x            : 'unit' num 0.2npc
# .. ..- attr(*, "valid.unit")= int 0
# .. ..- attr(*, "unit")= chr "npc"
# ..$ y            : 'unit' num 0.739npc
# .. ..- attr(*, "valid.unit")= int 0
# .. ..- attr(*, "unit")= chr "npc"
# ..$ just         : chr "centre"
# [...]

The grob object is a list containing various attributes, including the label attribute.

Extracting and Formatting Labels

We can extract the labels using the bracket function [[]], save them in two distinct temporary objects, and then format them using formatC.

tmp1 <- tmp2 <- lapply(V, [[, "label"])
tmp1[sapply(lapply(V, [[, "label"])), is.null)] <- NA
tmp1[] <- ifelse(is.na(as.numeric(tmp1)), NA,
                 formatC(as.numeric(tmp1), format="d", big.mark=","))
tmp2[!is.na(tmp1)] <- tmp1[!is.na(tmp1)]

In this code snippet, we first extract the labels using lapply. We then filter out any NA values and format the remaining numeric values using formatC, adding comma separators for big numbers.

Replacing Labels in the Grob Object

Finally, we replace the labels modified with big marks in the grob object using Map.

V <- class$<->(Map(`[[&lt;-`, V, "label", tmp2), "gList")

Plotting the Updated Grob Object

With the updated labels, we can now plot the grob object using grid.draw.

grid.newpage()
grid.draw(V)

Conclusion

In this example, we explored how to add comma separators for big numbers in a triple Venn diagram generated by the VennDiagram package. We caught the grob object, explored its structure, extracted and formatted labels, replaced them in the grob object, and finally plotted the updated Venn diagram.

Additional Resources

• Venn Diagrams in R: Learn more about creating Venn diagrams using the VennDiagram package.
• formatC() Function in R: Understand how to format numbers using formatC().

Step-by-Step Code

library(VennDiagram)

grid.newpage()
draw.triple.venn(
    area1 = 49644,
    area2 = 38697,
    area3 = 33281,
    n12 = 14221,
    n23 = 11026,
    n13 = 13635,
    n123 = 4242,
    category = c("DOGS", "CATS", "HORSES"),
    cex = 1.6,
    cat.cex = 1.8,
    lwd = 2,
    fill = c("blue", "pink1", "grey50")
)

V <- draw.triple.venn(...)  ## catch it in an object

tmp1 <- tmp2 <- lapply(V, [[, "label"])
tmp1[sapply(lapply(V, [[, "label"])), is.null)] <- NA
tmp1[] <- ifelse(is.na(as.numeric(tmp1)), NA,
                 formatC(as.numeric(tmp1), format="d", big.mark=","))
tmp2[!is.na(tmp1)] <- tmp1[!is.na(tmp1)]

V <- class$<->(Map(`[[&lt;-`, V, "label", tmp2), "gList")

grid.newpage()
grid.draw(V)

This code can be run in a R environment to generate the updated triple Venn diagram with comma-separated labels.

Last modified on 2023-08-05