Plot data frame's lists in ggplot2

Question

I have a data.table / data frame with lists as values. I would like to make a box or violin plot of the values, one violin/box representing one row of my data set, but I can't figure out how.

Example:

test.dt <- data.table(id = c('a','b','c'), v1 = list(c(1,0,10),1:5,3))
ggplot(data = test.dt, aes(x = as.factor(id), y = v1)) + geom_boxplot()

I get the following message:

Warning message: Computation failed in stat_boxplot(): 'x' must be atomic

So my guess is that maybe I should split the lists of the values to rows somehow. I.e.: the row with a as id would be transformed to 3 rows (corresponding to the length of the vector in v1) with the same id, but the values would be split among them.

Firstly I don't know how to transform the data.table as mentioned, secondly I don't know either if this would be the solution at all.

NRLP · Accepted Answer · 2018-12-05 11:07:38Z

2

Indeed, you need to unnest your dataset before plotting:

library(tidyverse)

unnest(test.dt) %>% 
ggplot(data = ., aes(x = as.factor(id), y = v1)) + geom_boxplot()

edited Dec 5, 2018 at 11:07

answered Dec 5, 2018 at 10:35

NRLP

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4 Comments

s__ Over a year ago

You can also put everything in a dplyr chain.

NRLP Over a year ago

The explanation was simpler in separate steps. But indeed, it's more elegant: unnest(test.dt) %>% ggplot(data = ., aes(x = as.factor(id), y = v1)) + geom_boxplot()

Newl Over a year ago

@Luminita Edited my question, thanks for pointing it out. I was trying to make a boxplot, indeed!

NRLP Over a year ago

In case the aim is a histogram of v1 (a histogram is a univariate tool as it plots the frequency of a variable): ggplot(data = test.dt, aes(x = v1)) + geom_histogram(). Otherwise, one may be interested in histograms by groups (here, ids) - which can be achieved with facetting: ggplot(data = test.dt, aes(x = v1)) + geom_histogram() + facet_wrap(~id)

Mojoesque · Accepted Answer · 2018-12-05 10:31:55Z

I believe what you are looking for is the very handy unnest() function. The following code works:

library(data.table)
library(tidyverse)

test.dt <- data.table(id = c('a','b','c'), v1 = list(c(1,0,10),1:5,3))
test.dt = test.dt %>% unnest()

ggplot(test.dt, aes(x = as.factor(id), y = v1)) + 
  geom_boxplot()

If you don't want to import the whole tidyverse, the unnest() function is from the tidyr package.

This is what unnest() does with example data:

> data.table(id = c('a','b','c'), v1 = list(c(1,0,10),1:5,3))
   id        v1
1:  a   1, 0,10
2:  b 1,2,3,4,5
3:  c         3
> data.table(id = c('a','b','c'), v1 = list(c(1,0,10),1:5,3)) %>% unnest()
   id v1
1:  a  1
2:  a  0
3:  a 10
4:  b  1
5:  b  2
6:  b  3
7:  b  4
8:  b  5
9:  c  3

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