Using dplyr to create summary proportion table with several categorical/factor variables

Question

I am trying to create one table that summarizes several categorical variables (using frequencies and proportions) by another variable. I would like to do this using the dplyr package.

These previous Stack Overflow discussions have partially what I am looking for: Relative frequencies / proportions with dplyr and Calculate relative frequency for a certain group.

Using the mtcars dataset, this is what the output would look like if I just wanted to look at the proportion of gear by am category:

    mtcars %>%
    group_by(am, gear) %>%
    summarise (n = n()) %>%
    mutate(freq = n / sum(n))

    #   am gear  n      freq
    # 1  0    3 15 0.7894737
    # 2  0    4  4 0.2105263
    # 3  1    4  8 0.6153846
    # 4  1    5  5 0.3846154

However, I actually want to look at not only the gears by am, but also carb by am and cyl by am, separately, in the same table. If I amend the code to:

    mtcars %>%
    group_by (am, gear, carb, cyl) %>%
    summarise (n = n()) %>%
    mutate(freq = n / sum(n))

I get the frequencies for each combination of am, gear, carb, and cyl. Which is not what I want. Is there any way to do this with dplyr?

EDIT

Also, it would be an added bonus if anyone knew of a way to produce the table I want, but with the categories of am as the columns (as in a classic 2x2 table format). Here is an example of what i'm referring to. It is from one of my previous publications. I want to produce this table in R, so that I can output it directly to a word document using RMarkdown:

Answer 1

One way to solve this, is to turn your data to a long(er) format. You can then use the same code to calculate the outcomes you want, with one extra group_by:

library(reshape2)
library(dplyr)

m_mtcars <- melt(mtcars,measure.vars=c("gear","carb","cyl"))

res <- m_mtcars %>%
  group_by(am, variable, value) %>%
  summarise (n = n()) %>%
  mutate(freq = n / sum(n))

Building on this, the desired output can be obtained using more reshaping and some string formatting

#make an 'export' variable
res$export <- with(res, sprintf("%i (%.1f%%)", n, freq*100))

#reshape again
output <- dcast(variable+value~am, value.var="export", data=res, fill="missing") #use drop=F to prevent silent missings 
#'silent missings'
output$variable <- as.character(output$variable)
#make 'empty lines' 
empties <- data.frame(variable=unique(output$variable), stringsAsFactors=F)
empties[,colnames(output)[-1]] <- ""

#bind them together
output2 <- rbind(empties,output)
output2 <- output2[order(output2$variable,output2$value),]

#optional: 'remove' variable if value present

output2$variable[output2$value!=""] <- ""

This results in:

   variable value          0         1
2      carb                           
7               1  3 (15.8%) 4 (30.8%)
8               2  6 (31.6%) 4 (30.8%)
9               3  3 (15.8%)   missing
10              4  7 (36.8%) 3 (23.1%)
11              6    missing  1 (7.7%)
12              8    missing  1 (7.7%)
3       cyl                           
13              4  3 (15.8%) 8 (61.5%)
14              6  4 (21.1%) 3 (23.1%)
15              8 12 (63.2%) 2 (15.4%)
1      gear                           
4               3 15 (78.9%)   missing
5               4  4 (21.1%) 8 (61.5%)
6               5    missing 5 (38.5%)

Answer 2

With tidyr/dplyr combination, here is how you would do it:

library(tidyr)
library(dplyr)

mtcars %>%
  gather(variable, value, gear, carb, cyl) %>%
  group_by(am, variable, value) %>%
  summarise (n = n()) %>%
  mutate(freq = n / sum(n))