ggplot - writing a function to create ggplot - how to assign parameter correctly?

Question

I cannot find an answer to this simple problem:

I want to create a ggplot. The aes parameter come partially from vector and partially are assigned directly.

names(mydt)
"gender"     "cat1"        "category_b"    "value"


category_a <- "cat1"

plot.sum <- mydt %>%
  dplyr::group_by(category_a, category_b) %>%
  ggplot(aes(x = category_a, y = N, fill = category_b)) +
  geom_bar(position="stack", stat="identity") 
plot.sum

This does not work and i get an error:

Error: Column category_a is unknown

I assume this is because R expects category_a to be a column in mydt and instead it gets an character item from a vector "cat1", which does not exist in mydt - correct me if i am wrong?

How can this be fixed?

The ultimate goal is to make this to a function:

make.plot.sum <- function (data, group_by1, group_by2, position){

data %>%
  dplyr::group_by(group_by1, group_by2) %>%
  ggplot(aes(x = group_by1, y = N, fill = group_by2)) +
    geom_bar(position="position", stat="identity") 
  plot.sum

  return(plot.sum)

}

make.plot.sum(mydt, category_a, category_b, stack)

Have you tried aes(x = {{group_by1}}, y = N, fill = {{group_by2}})? — teunbrand
– teunbrand, Commented Apr 12, 2020 at 20:53
@teunbrand i am not sure what the {{}} stand for, buut it seems like eit converts the group_by1 t plain text, but it was originally a factor with about 15 levels — Nneka
– Nneka, Commented Apr 12, 2020 at 21:32
Alright and aes(x = .data[[group_by1]], y = N, fill = .data[[group_by2]])? I think the post on this piece of nonstandard evaluation can be found here: tidyverse.org/blog/2019/06/rlang-0-4-0 — teunbrand
– teunbrand, Commented Apr 12, 2020 at 21:47

chemdork123 · Accepted Answer · 2020-04-12 21:04:17Z

1

You are correct: the issue is likely due to passing a character "cat1" to aes(), when aes() expects you to pass a column name (i.e. cat1 without any quotes). If you want to pass info to aes(... as a character, you can use aes_string(...) in place of aes(): just make sure that when you use aes_string(), all the parameters are character vectors, and for aes(), all parameters are references to column names in your dataframe.

Side Note: I'm not actually sure if you can combine aes() and aes_string(...), in case you are wondering... I've never tried it. So, like can you say aes(x=cat1), then aes_string(y='cat2')? Not sure.

answered Apr 12, 2020 at 21:04

chemdork123

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Comments

Conor Neilson · Accepted Answer · 2020-04-12 21:31:18Z

0

chemdorks123s answer is a great one - but it is worth pointing out that aes_string is considered soft decrecated in favor of new idioms.

In your situation, where you want the user to pass a column into aes, you can use curly braces ({{}}).

make.plot.sum <- function (data, group_by1, group_by2, position){

data %>%
  dplyr::group_by(group_by1, group_by2) %>%
  ggplot(aes(x = {{group_by1}}, y = N, fill = {{group_by2}})) +
    geom_bar(position="position", stat="identity") 
  plot.sum

  return(plot.sum)

}

There's a lot more info in one of the ggplot2 vignettes - Using ggplot2 in packages

answered Apr 12, 2020 at 21:31

Conor Neilson

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3 Comments

Nneka Over a year ago

as i was just commenting to @teunbrand who proposed this solution (see above), this acts as if the factor group_by1 had only one level, when it acttually has multiple leevels

Conor Neilson Over a year ago

Can you expand on what you expect the group_by to do? Its been a while since I've looked, but I dont think ggplot2 understands groups created by dplyr. Does it work like you expect outside of the function? If you're wanting to create multiple plots based on a factor level, it would make more sense to pass the grouping into a facet

Nneka Over a year ago

@Conoe Neilson it works fine, before when i use cat1 instead of instead of category_a in the plot. As soon as i use category_a <- cat1 , i get the error.

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