Combining 2 columns with values in R - r

Question

I'm working on a dataset about football. So I've made some time series analyses. I've calculated the amount of goals and the amount of goals in the previous month. Now I'm trying to plot it into a graph.
I'm trying to make a group bar chart with the goals of a certain month and from the previous month next to it.
This is the code that I'm using:
df_eredivisie %>%
group_by(month= month(date, label = TRUE)) %>%
summarise(goals = sum(FTHG + FTAG)) %>%
mutate(last = lag(goals, 1))
So this is the result (Sorry can't post pictures :/ ):
month goals last
Jan 69 NA
Feb 121 69
Mar 116 121
Apr 155 116
May 78 155
Aug 88 78
Sep 124 88
Oct 91 124
Nov 91 91
Dec 128 91
Could someone help me with the grouped bar chart? I've tried to combine the columns, so I could do fill and have the goals and last with different colours. But I couldn't figure out how to do that.

Answer 1

Your data need to be in long format, then it's simple:
library(ggplot2)
library(tidyverse)
df <- tribble(~month, ~goals, ~last,
"Jan", 69, NA,
"Feb", 121, 69,
"Mar", 116, 121,
"Apr", 155, 116,
"May", 78, 155,
"Aug", 88, 78,
"Sep", 124, 88,
"Oct", 91, 124,
"Nov", 91, 91,
"Dec", 128, 91)
df %>%
pivot_longer(cols = 2:3, names_to = "category") %>%
mutate(month = factor(month, levels = month.abb)) %>%
ggplot(aes(x = month, y = value, fill = category)) +
geom_col(position = "dodge")
#> Warning: Removed 1 rows containing missing values (geom_col).
Created on 2020-06-07 by the reprex package (v0.3.0)
If you reverse the factors, it looks like this:
df %>%
pivot_longer(cols = 2:3, names_to = "category") %>%
mutate(month = factor(month, levels = month.abb)) %>%
ggplot(aes(x = month, y = value, fill = forcats::fct_rev(category))) +
geom_col(position = "dodge")
#> Warning: Removed 1 rows containing missing values (geom_col).
Created on 2020-06-07 by the reprex package (v0.3.0)
So it works, but the second column does not add any information, as you can see the previous month right next to it...