# How to make a line graph using ggplot2

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You probably learned to make a line graph back in high school (or even middle school!). But the `ggplot`

R package can make these graphs come to life. Let’s take a look at how to do this.

First, we need interesting data. For this post, we will use this earth surface temperature data. This dataset is pre-processed so we can explore climate trends right off the bat. Your data may need some coaxing to get it in a form that can be plotted. But once you have the data cleaned and formatted there is so much you can do to visualize it with `ggplot`

.

Here let’s explore the temperature trends in Denmark. The dataset has four Danish cities: Aalborg, Aarhus, Copenhagen, and Odense. Temperatures begin in 1743 and continue through 2013.

The first call to `ggplot()`

defines the dataframe and assigns `Year`

to the x variable and `AverageTemperature`

to the y variable. The next call to `geom_point()`

creates a point for each datum. Next, the `geom_line()`

call adds a line between points. Here we made the line ‘steelblue’ to stand out. We use `scale_x_discrete()`

to display specific years on the x-axis which makes it easier to read the plot. Then `facet_wrap()`

makes a separate panel for each city. The last two steps are `labs()`

to add labels and `theme()`

to adjust the appearance.

require(ggplot2) line_graph <- ggplot(df_yearly, aes(x = Year, y = AverageTemperature, group = 1)) + geom_point() + geom_line(color="steelblue") + scale_x_discrete(breaks=seq(1743, 2013, 50)) + facet_wrap(~City) + labs(subtitle = "Mean Annual Temperatures", x = "Year", y = "Average Temperature") + theme_minimal() + theme(text = element_text(size = 20))

Thanks for reading and I hope this helps your R project! If there is a topic you would like me to explore, drop me a line through the contact me page.

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