ggplot and dplyr and column name as string

Question

I would like to process data frame through dplyr and ggplot using column names in form of string. Here is my code

library(ggplot2)
library(dplyr)
my_df <- data.frame(var_1 = sample(c('a', 'b', 'c'), 1000, replace = TRUE),
                    var_2 = sample(c('d', 'e', 'f'), 1000, replace = TRUE))

name_list = c('var_1', 'var_2')

for(el in name_list){
  pdf(paste(el, '.pdf', sep =''))
    test <- my_df %>% group_by(el) %>% summarize(count = n())
    ggplot(data = test, aes(x = el, y = count)) + geom_bar(stat='identity')
  dev.off()
}

The above code obviously does not work. So I tried different things like UQ and as.name. UQ creates column with extra quotes and ggplot does not understand it with aes_string. Any suggestions?

I can use for (el in names(my_df)) with filtering, but would prefer to work with strings.

UPDATE Here are detailed messages/errors that I got:

for(el in name_list){
  pdf(paste(el, '.pdf', sep =''))
    test <- my_df %>% group_by(!!el) %>% summarize(count = n())
    ggplot(data = test, aes_string(x = el, y = 'count')) + geom_bar(stat='identity')
  dev.off()
}

The above code generate empty files.

for(el in name_list){
  pdf(paste(el, '.pdf', sep =''))
    test <- my_df %>% group_by(UQ(el)) %>% summarize(count = n())
    ggplot(data = test, aes_string(x = el, y = 'count')) + geom_bar(stat='identity')
  dev.off()
}

The above code also generates empty files

for(el in name_list){
  pdf(paste(el, '.pdf', sep =''))
    test <- my_df %>% group_by(as.name(el)) %>% summarize(count = n())
    ggplot(data = test, aes_string(x = el, y = 'count')) + geom_bar(stat='identity')
  dev.off()
}

produces

Error in mutate_impl(.data, dots) : 
  Column `as.name(el)` is of unsupported type symbol

Related: (dplyr) stackoverflow.com/questions/45442513/… (ggplot) stackoverflow.com/questions/15458526/… — MrFlick
– MrFlick, Commented Sep 22, 2017 at 20:26
Show your attempts with UQ and aes_string. Give the error messages you got. Otherwise this each part of this is just a duplicate of a simpler question. — MrFlick
– MrFlick, Commented Sep 22, 2017 at 20:27

MrFlick · Accepted Answer · 2017-09-22 21:05:01Z

4

You need to UQ (or !!) the name/symbol. For example

for(el in name_list){
  pdf(paste(el, '.pdf', sep =''))
  test <- my_df %>% group_by(UQ(as.name(el))) %>% summarize(count = n())
  print(ggplot(data = test, aes_string(x = el, y = 'count')) + geom_bar(stat='identity'))
  dev.off()
}

edited Sep 22, 2017 at 21:05

answered Sep 22, 2017 at 20:52

MrFlick

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1 Comment

MrFlick Over a year ago

Oh. You need to print() the ggplot object inside a loop with this method. Didn't think about that problem because I missed that part.

pogibas · Accepted Answer · 2017-09-22 20:45:58Z

2

I made two changes to your code:

To "group by" variable in dplyr use group_by_ instead of group_by;
To call variable in ggplot2 use aes_string or get(variable);

I also added minor changes (e.g. ggsave to save plots).

library(ggplot2)
library(dplyr)
my_df <- data.frame(var_1 = sample(c('a', 'b', 'c'), 1000, replace = TRUE),
                    var_2 = sample(c('d', 'e', 'f'), 1000, replace = TRUE))

name_list = c('var_1', 'var_2')

for(el in name_list){
    p <- my_df %>% 
         group_by_(el) %>% 
         summarize(count = n()) %>%
         ggplot(aes(x = get(el), y = count)) +
             geom_bar(stat = "identity")
    ggsave(paste0(el, ".pdf"), p)
}

answered Sep 22, 2017 at 20:45

pogibas

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2 Comments

user1700890 Over a year ago

ggsave made all the difference, but without ggsave it does not work

winni2k Over a year ago

The reason ggsave is needed for this to work is that get() is evaluated lazily. You need ggsave inside the loop to make sure get() pulls the correct string. I found that if I use aes_string instead of get() then things are fine. I.e.: ggplot(aes_string(x = el, y = "count")) ...

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