Create geom_tile plot with two dataframes

Question

Below is R code that attempts to create a heat map using geom_tile. Within my plot, I need to plot an outline of a box and a separate pair of x//y coordinates (titled platelocside and platelocheight in the code) that also have a fill (titled exitspeed in code) to complete the heat map. Here is the current structure of my data frame that I want to plot (labeled as "df" in the code).

structure(list(platelocheight = c(2.594, 3.803, 3.254, 3.599, 
3.617, 3.297, 2.093, 3.611, 2.842, 3.316, 2.872, 3.228, 3.633, 
4.28, 3.309, 2.8, 2.632, 3.754, 2.207, 3.604, 3.443, 2.188, 3.452, 
2.553, 3.382, 3.067, 2.986, 2.785, 2.567, 3.804), platelocside = c(0.059, 
-1.596, -0.65, -0.782, -0.301, -0.104, 0.057, -0.807, 0.003, 
1.661, 0.088, -0.32, -1.115, -0.146, -0.364, -0.952, 0.254, 0.109, 
-0.671, -0.803, -0.212, -0.069, -0.09, -0.472, 0.434, 0.337, 
0.723, 0.508, -0.197, -0.635), exitspeed = c(69.891, 73.352, 
83.942, 85.67, 79.454, 85.277, 81.078, 73.573, 77.272, 59.263, 
97.343, 91.436, 76.264, 83.479, 47.576, 84.13, 60.475, 61.093, 
84.54, 69.959, 88.729, 88.019, 82.18, 83.684, 86.296, 90.605, 
79.945, 59.899, 62.522, 77.75)), .Names = c("platelocheight", 
"platelocside", "exitspeed"), row.names = c(NA, 30L), class = "data.frame")
> 

When I run the code, I am able to get the outline of the box in my output, but the other data frame (title df) did not plot. Does anyone know who to use geom_tile that will be able to plot two separate dataframes? Thanks in advance!

library(RODBC)
library(ggplot2)


con=odbcConnect('ID',uid='username', pwd = 'password')

df=sqlQuery(con,"select platelocheight, platelocside, exitspeed from tm_sample where pitchcall='InPlay' 
and exitspeed is not null")

topKzone <- 3.5
botKzone <- 1.6
inKzone <- -0.95
outKzone <- 0.95
kZone <- data.frame(
  x=c(inKzone, inKzone, outKzone, outKzone, inKzone),
  y=c(botKzone, topKzone, topKzone, botKzone, botKzone)
)

ggplot(kZone, aes(x,y)) +
  geom_tile(data=df, aes(x=platelocside, y=platelocheight, fill= exitspeed)) +
  scale_fill_distiller(palette = "Spectral") +
  geom_path(lwd=1.5, col="black") +
  coord_fixed() 

Answer 1

The problem is that not in the use of two dataframes, but rather in the implementation of geom_tile() itself.

If you swap for geom_tile for a different geom, say geom_point or geom_hex for example, you'd see that the plot is rendered perfectly:

library(ggplot2)
ggplot(kZone, aes(x,y)) +
  geom_hex(data=df, aes(x=platelocside, y=platelocheight, col=exitspeed)) +
  scale_fill_distiller(palette = "Spectral") +
  geom_path(lwd=1.5, col="black") +
  coord_fixed() 

Produces this:

Understanding geom_tile

geom_tile is not a good choice with your data because you're using a continuous x and y scale and that makes it a more viable choice with something like a scatterplot as compared to a heatmap-like graphic.

You can see an example:

ggplot(mtcars, aes(x=as.factor(gear), y=as.factor(cyl), fill=hp))+
    geom_tile()

Compared to when you were to call it on two continuous variables:

ggplot(mtcars, aes(x=wt, y=mpg, fill=hp))+
    geom_tile()

You'll get tiles that are so small in effect it looks like nothing was plotted.

Going back to your question, the df that you're using has platelocside and platelocheight both as numeric, continuous variables. That makes geom_hex a less-than-ideal choice. If you do insist on using geom_tile then I would use one of the two solutions:

Solution 1

Use col instead of fill to get points instead of tiles (since the x and y are not factor variables)

library(ggplot2)
ggplot(kZone, aes(x,y)) +
  geom_tile(data=df, aes(x=platelocside, y=platelocheight, col=exitspeed), size=4) +
  scale_fill_distiller(palette = "Spectral") +
  geom_path(lwd=1.5, col="black") +
  coord_fixed() 

Solution 2

Make x and y a factor variable:

df$h <- round(df$platelocheight)
df$s <- round(df$platelocside)

ggplot(kZone, aes(x,y)) +
  geom_tile(data=df, aes(x=s, y=h, fill=exitspeed)) +
  scale_fill_distiller(palette = "Spectral") +
  geom_path(lwd=1.5, col="black") +
  coord_fixed()