Create grid heatmap with axis corresponding to intervals in R-CodePudding

I want to create a ggplot heatmap in R with the use of the command

ggplot()                           
  geom_tile()

I have the following data

t_1 = c(-1,0,1,4)
t_2 = c(-2,-1,3)
W = c(1,10,3,4,17,9)

The t_1 corresponds to intervals in x-axis, i.e. corresponds to (-1,0), (0,1), (1,4). And t_2 to intervals in the y-axis, i.e. (-2,-1),(-1,3). Based on these intervals a grid of 6 squares is created and on each square a value of W corresponds. So the value W[1] corresponds to the square (-1,0),(-2,-1), the value W[2] corresponds to the square (-1,0),(-1,3) etc.

So, how do I create that kind of heatmap??

CodePudding user response：

Here's a way that allows you to still use geom_tile by using your vectors to provide the height and width aesthetics:

library(ggplot2)

d <- cbind(expand.grid(y = diff(t_2)/2   head(t_2, -1), 
                       x = diff(t_1)/2   head(t_1, -1)), W)

ggplot(d, aes(x, y, fill = W))   
  geom_tile(height = rep(diff(t_2), 3), width = rep(diff(t_1), each = 2))

CodePudding user response：

You first have to create a data.frame containing the coordinates of your six squares. Afterwards you could plot your heat map using geom_rect:

t_1 = c(-1,0,1,4)
t_2 = c(-2,-1,3)
W = c(1,10,3,4,17,9)

# Create a df containig coordinates of the squares
grid <- data.frame(
  xmin = rep(rev(rev(t_1)[-1]), 2),
  xmax = rep(t_1[-1], 2),
  ymin = rep(rev(rev(t_2)[-1]), each = 3),
  ymax = rep(t_2[-1], each = 3),
  fill = W
)
grid
#>   xmin xmax ymin ymax fill
#> 1   -1    0   -2   -1    1
#> 2    0    1   -2   -1   10
#> 3    1    4   -2   -1    3
#> 4   -1    0   -1    3    4
#> 5    0    1   -1    3   17
#> 6    1    4   -1    3    9

library(ggplot2)

ggplot(grid)  
  geom_rect(aes(xmin = xmin, xmax = xmax, ymin = ymin, ymax = ymax, fill = fill))