I encountered this problem when I was learning nonlinear regression with R : there is this function "plotfit" in package "nlstools",which "displays a superimposed plot of the dependent variable versus one the independent variables together with the fitted model.",but when I execute the example given in the help page, it keeps saying that :
plotfit(nls1, smooth = TRUE)
Error in form[[3]] : object of type 'symbol' is not subsettable can anybody tell me what this means and how to fix it ?