Count line graphs in ggplot2

Question

I am new to R/ggplot2 and am trying to create a line graph of counts (or percentages, it doesn't matter) for responses to 6 stimuli in ggplot in R. The stimuli should go across the x-axis, and the count on the y-axis. One line will represent the number of participants who responded with a preposition, and the other line will represent the number of participants who responded with a number.

I believe that ggplot with geom_line() requires an x and y (where y is the count or percentage).

Should I create a new data frame with count so that I can use ggplot? And then, a subquestion would be how do I count responses based on the stimulus data (so, how do I count response based on another column in the data frame, or how many preposition responses for stimulus 1, how many number responses for stimulus 1, how many preposition responses for stimulus 2, etc. Maybe with some kind of if statement?)?

or

Is there a way to automatically produce these counts in ggplot?

Of course, it's entirely possible that I'm going about this the wrong way entirely.

I've tried to search this, but cannot find anything. Thank you so much.

With a categorical x variable, I would recommend using grouped bars instead of lines, but maybe that's just me. In ggplot, this will also have the advantage of automating the counting, as the default behavior for geom_bar() is to use stat="bin" (which counts the number of cases in each group) for the y-axis. — ulfelder
– ulfelder, Commented Sep 14, 2015 at 21:14
You can use stat = "bin" in geom_line if you want ggplot2 to count up the number per group for you. Lots of info about aggregating data by group on SO - see here and here for a start. — aosmith
– aosmith, Commented Sep 14, 2015 at 21:49
Thank you for the help! This was very useful. I ended up making a frequency table and turning it into a data frame and plotting that with ggplot. — Lisa
– Lisa, Commented Sep 15, 2015 at 14:24
Good job figuring out an approach that worked for you. You can go ahead and write up an answer for how you approached the problem so the question can be marked as solved. — aosmith
– aosmith, Commented Sep 15, 2015 at 15:11

Lisa · Accepted Answer · 2015-09-15 16:34:32Z

1

As I said in my comment, I ended up creating a frequency table and using ggplot to plot the resulting data frame. Here's the code below!

# creates data frame
resp <- c("number", "number", "preposition", "number")
sound <- c(1, 1, 2, 2)
df <- data.frame(resp, sound) 

# creates frequency table
freq.table <- prop.table((xtabs(~resp+sound, data=df)), 2)
freq.table.df <- as.data.frame(freq.table)

# plots lines based on frequency
ggplot(freq.table.df, aes(sound, Freq, group=resp, color=resp)) + 
  geom_line()

answered Sep 15, 2015 at 16:34

Lisa

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