grade.parse: Parse Input
In grade: Binary Grading functions for R.

Description Usage Arguments Details Value Note See Also Examples

View source: R/grade.parse.R

Parse input, returning either NULL or a vector of the values.

grade.isscalar(x, usena=FALSE, useinf=FALSE, quiet=TRUE)

grade.parse(ans, useeval=TRUE, usena=FALSE, useinf=FALSE, quiet=TRUE)
grade.parseset(ans, useeval=TRUE, usena=FALSE, useinf=FALSE, quiet=TRUE)
grade.parsechunk(ans, useeval=TRUE, usena=FALSE, useinf=FALSE, quiet=TRUE)

`x`	argument for grade.isscalar to check
`ans`	input to parse. Can be a `string` or a vector
`useeval`	`TRUE` or `FALSE` indicates whether or not to use 'eval' on strings
`usena`	`TRUE` or `FALSE` indicating whether or not `NA` is an accepted value
`useinf`	`TRUE` or `FALSE` indicating whether or not `Inf` and `-Inf` are accepted values
`quiet`	`TRUE` or `FALSE`. If `TRUE` there are more warning messages when checks fail. Can be helpful for debugging.

grade.isscalar checks to see if x is a finite numeric scalar (vector of length 1). If usena=TRUE, NA is also accepted. If useinf=TRUE, Inf and -Inf are also accepted.

Input to the grade.parse functions can be a string or a vector. grade.parsechunk will only return scalars, the other two will return a vector. All three check return values using grade.isscalar on each element.

grade.parse delegates character types to either grade.parsechunk or grade.parseset. If the string contains any of the characters '[', ']', '(', ')', or ',' the string is sent to grade.parseset. Otherwise it is sent to grade.parsechunk.

If x is a character, grade.parsechunk checks for any of the forbidden characters '[', ']', '(', ')', or ','. If any are found grade.parsechunk refuses to evaluate the string.

If x is a character, grade.parsechunk makes sure that it looks like a vector or set. I.e. it starts with an open bracket or parenthesis and ends with a close bracket or parenthesis. No other brackets or parenthesis are allowed. The middle is expected to be a comma delimited list. See the examples for more clarification.

If useeval=TRUE, text elements are evaluated using eval. If useeval=FALSE text elements are coerced using as.numeric. eval is more forgiving to input, i.e. eval of text input '1/2' returns .25, but as.numeric of text '1/2' returns NA. However, eval does leave an opening for unchecked code to be run in R. Text containing parenthesis or brackets is not put into either eval or as.numeric by the grade.parse functions, but there is still a risk. If you are concerned, set useeval=FALSE.

grade.parse and grade.parseset returns either a vector of the values, or NULL if the input was not valid.

grade.parsechunk returns either a single value, or NULL if the input was not valid.

grade.isscalar returns TRUE if x is a scalar (vector of length 1), FALSE otherwise.

The grade main page contains a discussion of the common parameters correctans, studentans, useeval, usena, useinf, quiet.

grade grade.set grade.number

grade.parse("[1, 2, 3]") # returns c(1,2,3)
grade.parse("[NA, 1, 2]") # returns NULL
grade.parse("[NA, 1, 2]", usena=TRUE) # returns c(NA, 1, 2)
grade.parse("[pi]") # returns 3.141....
grade.parse("[pi]", useeval=FALSE) # returns NULL

grade.parsechunk("1") # 1
grade.parsechunk(",1") # NULL
grade.parsechunk("[1]", quiet=FALSE) # NULL, with error message

grade.parseset("[1,2,3]") # c(1,2,3)

grade.isscalar(1) # TRUE
grade.isscalar(c(1,2)) # FALSE
grade.isscalar(NA) # FALSE
grade.isscalar(NA, usena=TRUE) # TRUE
grade.isscalar(Inf) # FALSE
grade.isscalar(Inf, useinf=TRUE) # TRUE