# Manipulate the component parts of formulas, expressions, calls, name/symbols and list and vectors of such objects. `lhs, rhs, op, and op.type` retrieve the various parts of R formulas, calls, expressions, names/symbols. These functions were designed to greatly facilitate symbolic manupulation using native R objects. Also provided are methods to handle list of these objects. methods ```r lhs(x, ...) ## S4 method for signature 'call' lhs(x) ## S4 method for signature 'formula' lhs(x) ## S4 method for signature 'expression' lhs(x, ...) ## S4 method for signature 'list' lhs(x, ...) lhs(x) <- value ## S4 replacement method for signature 'call' lhs(x) <- value ## S4 replacement method for signature 'formula' lhs(x) <- value .replace.lhs.plural(x, value) ## S4 replacement method for signature 'expression' lhs(x) <- value ## S4 replacement method for signature 'list' lhs(x) <- value op(x) ## S4 method for signature 'formula' op(x) ## S4 method for signature 'call' op(x) ## S4 method for signature 'name' op(x) ## S4 method for signature 'expression' op(x) ## S4 method for signature 'list' op(x) op(x) <- value ## S4 replacement method for signature 'call' op(x) <- value ## S4 replacement method for signature 'formula' op(x) <- value .replace.op.plural(x, value) ## S4 replacement method for signature 'expression' op(x) <- value ## S4 replacement method for signature 'list' op(x) <- value rhs(x, ...) .rhs.singular(x) ## S4 method for signature 'call' rhs(x) ## S4 method for signature 'formula' rhs(x) ## S4 method for signature 'expression' rhs(x, ...) ## S4 method for signature 'list' rhs(x, ...) rhs(x) <- value .replace.rhs.singular(x, value) ## S4 replacement method for signature 'call' rhs(x) <- value ## S4 replacement method for signature 'formula' rhs(x) <- value .replace.rhs.plural(x, value) ## S4 replacement method for signature 'expression' rhs(x) <- value ## S4 replacement method for signature 'list' rhs(x) <- value ``` ## Arguments - `x`: object from where to get/set the lhs/rhs - `...`: arguments passed to additional methods - `value`: the value to set for the lhs/rhs ## Returns Value depends on the argument. ## Details `lhs` retrieves the left-hand side `rhs` retrieves the right-hand side `op` retrieves the operation `op.type` returns the type operator There are also functions `lhs.vars` and `rhs.vars`. Like `all.vars`, these functions interpret the variables on the left-hand and right-hand sides respectively. These are simple functions for extracting the left-hand side, right-hand side, operator and operator type from formulas, expressions, calls, names/symbols and list containing these objects. lhs, rhs are only defined for formulas and calls ( and list and expressions ) that are defined with either one of the relational or tilde ('~') operators. If the object does not contain one of these operators, it will fail with a warning. The defined operator types are defined by the operator.tools package: See `operators` and `setOperator` The `lhs.vars` and `rhs.vars` methods, return the variables used on the lhs and rhs, respectively. If special formula variables are used, such as '.', a data.frame or environment must also be provided such that the variable list may be properly infered. ## Note Methods for the non-standard "`<-`" class exist and are not included in the usage documentation because CRAN does not support S4 documentation for this class. ## Examples ```r # FORMULA f <- A + B ~ C + D lhs(f) lhs(f) <- quote( E / F ) rhs(f) rhs(f) <- quote( G + H ) op(f) op(rhs(f)) op( quote(A) ) # NULL: op.type(f) # ONE-SIDED FORMULA f <- ~ A # lhs(f) # NULL rhs(f) # A # EXPRESSION e <- expression( A + B == C + D ) lhs(e) rhs(e) op(e) op.type(e) # CALL c <- quote( A + B > C + D ) lhs(c) lhs(c) <- quote(E) rhs(c) op(c) op.type(c) # ASSIGNMENT a <- quote( A <- B ) lhs(a) rhs(a) op(a) op.type(a) ``` ## See Also terms, all.vars, all.names, `operators` ## Author(s) Christopher Brown

formula.parts function