CODEWITHSUNDEEP
rformulatilde
Arklur
Arklur

Reputation: 183

Tilde operator without left side

rxHistogram(~fare_amount, data = inDataSource, title = "Fare Amount Histogram")

I've found many answers about what the ~ operator is used for, but there is always a left side for the operator in the answers. What if there is none? The sample was taken from here.

Upvotes: 1

Views: 584

Answers (1)

loki
loki

Reputation: 10340

"The left-hand side is optional, and one-sided formulae are used in some contexts." (?`~`)

If you compare the two following examples of plot you will see, that the plots differ from each other. While the first plot shows a horizontal density-like distribution of the values of carat the second plot uses the index of each row to plot the carat values. 

plot(~carat, data = ggplot2::diamonds, main = "With tilde", pch = 15, col = "#00000010")
plot(ggplot2::diamonds$carat, main = "NO tilde", pch = 15, col = "#00000010")

However, in some (cf. quote above) contexts like linear models for example, the left side is not optional and missing it will cause an error:

lm(~carat, data = ggplot2::diamonds)

Error in lm.fit(x, y, offset = offset, singular.ok = singular.ok, ...) : incompatible dimensions

Intentionally in cases like lm the tilde is used to express formulas (in this case the dependent or independent variables). As we can see in ?formula:

"The ~ operator is basic in the formation of such models. An expression of the form y ~ model is interpreted as a specification that the response y is modelled by a linear predictor specified symbolically by model."

We can also see that (?formula):

"There is a formula method for data frames. If there is only one column this forms the RHS with an empty LHS. For more columns, the first column is the LHS of the formula and the remaining columns separated by + form the RHS."

For your specific MS example:

The function description of rxHistogram states that:

" It should take the form of ~x|g1 + g2 where g1 and g2 are optional conditioning factor variables and x is the name of a variable or an on-the-fly factorization F(x). Other expressions of x are not supported."

Upvotes: 1

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