using parse(text= )

Question

I thought I understood eval(parse(text = )) but I am getting an error. I have a string named plotString that has been constructed using a for loop. If I print it out, it looks like this:

plotString
[1] "emo_plot[[1]],sentiment_plot[[1]],emo_plot[[2]],sentiment_plot[[2]],emo_plot[[3]],sentiment_plot[[3]],emo_plot[[4]],sentiment_plot[[4]],emo_plot[[5]],sentiment_plot[[5]],emo_plot[[6]],sentiment_plot[[6]],emo_plot[[7]],sentiment_plot[[7]],emo_plot[[8]],sentiment_plot[[8]],emo_plot[[9]],sentiment_plot[[9]],emo_plot[[10]],sentiment_plot[[10]]"

The end goal is to put it as the first argument in

pairPlot <- ggarrange( eval(parse(text=plotString)) + rremove("x.text"), labels = c("A", "B", "C", "D"), ncol = 6, nrow = 4)

But simply running it in

parse(text=plotString)

gives this error

Error in parse(text = plotString) : <text>:1:14: unexpected ','
1: emo_plot[[1]],
                 ^

and this

eval(parse(text=plotString))

gives, of course, the same

Error in parse(text = plotString) : <text>:1:14: unexpected ','
1: emo_plot[[1]],
                 ^

and this

pairPlot <- ggarrange( eval(parse(text=plotString)) + rremove("x.text"), labels = c("A", "B", "C", "D"), ncol = 6, nrow = 4)

gives, of course, the same

Error in parse(text = plotString) : <text>:1:14: unexpected ','
1: emo_plot[[1]],
                 ^

I have read that the text needs to evaluate to an R expression and I guess plotString is not an R expression. If that is the issue, how can I get the entry before the plus(+) sign in ggarrange() to be something like

emo_plot[[1]],sentiment_plot[[1]],emo_plot[[2]],sentiment_plot[[2]] 

Thank you.

Answer 1

parse() parses full expressions. That is, the code that you pass it must be syntactically valid self-contained R code. You can’t pass it fragments. Even if you could do that, you can’t eval() fragments either; once again, the expression you pass to eval() must be self-contained, complete, valid R code.

I’d generally be wary of any use of eval(parse(…)) in code; it’s usually solving the wrong problem.

In your case, where are you getting the input from? Unless the data comes from outside R, it’s almost certainly a better solution to store and manipulate the data as a list of expressions, not as a string. Then you can use it via do.call():

do.call('ggarrange', list_of_plots)