Question

我有一个公式作为字符向量，并希望在curve中使用它。

curve(-8*cos(2*x), 0, 10) #works as expected
formula <- "-8*cos(2*x)"

# nothing works

curve(formula, 0, 10)
# Error in formula.default(x) : invalid formula

curve(eval(formula), 0, 10)
# Error in curve(eval(formula), 0, 10) : 
#  'expr' must be a function, or a call or an expression containing 'x'

curve(as.expression(formula), 0, 10)
# Error in curve(as.expression(formula), 0, 10) : 
#  'expr' must be a function, or a call or an expression containing 'x'

curve(eval(as.expression(formula)), 0, 10)
# Error in curve(eval(as.expression(formula)), 0, 10) : 
#  'expr' must be a function, or a call or an expression containing 'x'

curve(parse(text = formula), 0, 10)
# Error in curve(parse(text = formula), 0, 10) : 
#  'expr' must be a function, or a call or an expression containing 'x'

curve(eval(parse(text = formula)), 0, 10)
# Error in curve(eval(parse(text = formula)), 0, 10) : 
#  'expr' must be a function, or a call or an expression containing 'x'

我的问题
我怎样才能做到这一点？

Answer 1

一种可能性是简单地用函数包装，

curve((function(x) eval(parse(text=formula)))(x), 0, 10)

如何在曲线（）中使用公式作为字符向量

1 个答案: