We’ll use a subset of the climate data and create a new column called pos, which indicates whether the value is positive or negative:
library(gcookbook) # Load gcookbook for the climate data set library(dplyr) climate %>% climate_sub <- filter(Source == "Berkeley" & Year >= 1900) %>% mutate(pos = Anomaly10y >= 0) climate_sub#> Source Year Anomaly1y Anomaly5y Anomaly10y Unc10y pos #> 1 Berkeley 1900 NA NA -0.171 0.108 FALSE #> 2 Berkeley 1901 NA NA -0.162 0.109 FALSE #> 3 Berkeley 1902 NA NA -0.177 0.108 FALSE #> ...<99 more rows>... #> 103 Berkeley 2002 NA NA 0.856 0.028 TRUE #> 104 Berkeley 2003 NA NA 0.869 0.028 TRUE #> 105 Berkeley 2004 NA NA 0.884 0.029 TRUE
Once we have the data, we can make the graph and map pos to the fill color, as in Figure 3.11. Notice that we use position=“identity” with the bars. This will prevent a warning message about stacking not being well defined for negative numbers:
ggplot(climate_sub, aes(x = Year, y = Anomaly10y, fill = pos)) + geom_col(position = "identity")
There are a few problems with the first attempt. First, the colors are probably the reverse of what we want: usually, blue means cold and red means hot. Second, the legend is redundant and distracting.
We can change the colors with
scale_fill_manual() and remove the legend with
guide = FALSE, as shown in Figure 3.12. We’ll also add a thin black outline around each of the bars by setting
colour and specifying
size, which is the thickness of the outline (in millimeters):
ggplot(climate_sub, aes(x = Year, y = Anomaly10y, fill = pos)) + geom_col(position = "identity", colour = "black", size = 0.25) + scale_fill_manual(values = c("#CCEEFF", "#FFDDDD"), guide = FALSE) #> Warning: Using `size` aesthetic for lines was deprecated in ggplot2 3.4.0. #> ℹ Please use `linewidth` instead. #> This warning is displayed once every 8 hours. #> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was #> generated. #> Warning: The `guide` argument in `scale_*()` cannot be `FALSE`. This was deprecated #> in ggplot2 3.3.4. #> ℹ Please use "none" instead. #> This warning is displayed once every 8 hours. #> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was #> generated.