I'm trying to make a function that calls to a column in the data table supplied as one of the arguments below:

df <- read.table(text = "x1 x2 y
CA 20 50
CA 30.5 100
CA 40.5 200
AZ 20.12 400
AZ 25 500
OR 86 600
OR 75 700
OR 45 800", header = TRUE)

df$x1 <- as.factor(df$x1)

library(data.table)

make_freq <- function(df, var_name){
  
  df <- df 
  setDT(df)
  
  
  tb <- df[, .N, by = var_name][,prop_ := round(((N/sum(N))*100), digits = 0)][order(var_name)]
  
  gg1 <- ggplot(tb, aes(x = var_name, y = prop_))  
    geom_bar(width = .35, stat = "identity", color = "darkblue", fill = "darkblue")  
    ggtitle(paste0("var_name"))  
    theme_bw()  
    theme(plot.title = element_text(size = 10))  
    theme(axis.text.x = element_text(angle = 45)) 
  
  return(list(figure = gg1))
}

make_freq(df = df, var_name = x1)

Ideally I want to be able to run the function so that I can create the ggplot figure for any categorical variable I want using the var_name argument. I'm getting Object x1 not found error which makes me think I need to quote or unquote the var_name argument within the function or something.

CodePudding user response：

Yes, if you would like to use non-standard evaluation you will need to quote the var_name argument. Simply add:

var_name <- substitute(var_name)

to the top of the function. Note that the default x axis label in this case will be var_name. If you would like it to default to whatever is passed as var_name you will need to do a couple of extra steps. Change the top of the function to:

  x <- enquo(var_name)
  var_name <- substitute(var_name)

Then modify the tb line.

  tb <- df[, .N, by = eval(deparse(var_name))][,prop_ := round(((N/sum(N))*100), digits = 0)][order(eval(var_name))]

Then in ggplot():

gg1 <- ggplot(tb, aes(x = !!x, y = prop_))   ...

CodePudding user response：

1. You should to quote the x1 cause you have no this object (this is the name of column).
2. Argument by in data.table object may be character and df[, .N, by = var_name] is good code. But [order(var_name)] is wrong. You can use [order(get(var_name))].
3. Cause var_name is character we need to change var_name to get(var_name) in ggplot.

Full code:

make_freq <- function(df, var_name){
    
    df <- df 
    setDT(df)
    
    
    tb <- df[, .N, by = var_name][,prop_ := round(((N/sum(N))*100), digits = 0)][order(get(var_name))]
    
    gg1 <- ggplot(tb, aes(x = get(var_name), y = prop_))  
        geom_bar(width = .35, stat = "identity", color = "darkblue", fill = "darkblue")  
        ggtitle(paste0("var_name"))  
        theme_bw()  
        theme(plot.title = element_text(size = 10))  
        theme(axis.text.x = element_text(angle = 45)) 
    
    return(list(figure = gg1))
}


make_freq(df = df, var_name = "x1")