parse() Function in R

The parse() function in R programming language is used to return the parsed but unevaluated expression of a given expression in an expression, a “list” of calls. Also, this function converts an R object of the character class to an R object of the expression class.

Syntax: parse(file = “”,  n = NULL, text = NULL, prompt = “?”, keep.source = getOption(“keep.source”), encoding = “unknown”)

Parameters:

•    file (optional): This is a character string specifying the file’s name or the URL from which to read the expressions.
•    n (optional): This is an integer representing the maximum number of expressions to be parsed.
• text (required): This is a character vector representing the text to be parsed.
• prompt (optional): This represents the prompt to return when parsing from the keyboard.
• keep.source (optional): This takes a logical value (True or False) indicating whether the source information is kept or not.
• encoding (optional): This is the encoding that is assumed for the input strings.

Returns: The parse() function returns an object type “expression”.

Example 1:

In this example, we will convert the provided data object from a character class to an expression class using the parsed function. Further, we will evaluate the converted expression in the R programming language.

R

# creating a character string
x <-"50/5"

# Changing the character to
# expression class
y <- parse(text = x)

# verifying the object type
class(y)

# evaluating the expression
eval(y)

Output:

'expression'
10

Example 2:

In this example, we will convert the provided data object of a character class with a long-expression to an expression class using the parsed function. Further, we will evaluate the converted expression in the R programming language.

R

# creating a character string
x1 <-"50/5+5^5-9*2"

# Changing the character to
# expression class
y1 <- parse(text = x1)

# verifying the object type
class(y1)

# evaluating the expression
eval(y1)

Output:

'expression'
3117

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