r - styleColorBar Center and shift Left/Right dependent on Sign

Question

I am looking to create bars that when using DT's datatable appear in the middle of the cells of a column and reach out left or right depending on whether the value in the cell is positive or negative.

I have tried using the function styleColorBar and changing the argument backgroundPosition to 'left' or 'center' however with each try the bars still appear to the right of the cell and always go to the left.

I can't find an example from R code, but have attached an example of what can be done on Excel; the colours aren't necessary but if included that would be a bonus.

Answer 1

You could make a custom styleColorBar function that uses the CSS gradients (same as the original styleColorBar) to make the kind of bars you want.

Here is an example (sorry for the long line, adding new lines breaks the CSS):

color_from_middle <- function (data, color1,color2) 
{
  max_val=max(abs(data))
  JS(sprintf("isNaN(parseFloat(value)) || value < 0 ? 'linear-gradient(90deg, transparent, transparent ' + (50 + value/%s * 50) + '%%, %s ' + (50 + value/%s * 50) + '%%,%s  50%%,transparent 50%%)': 'linear-gradient(90deg, transparent, transparent 50%%, %s 50%%, %s ' + (50 + value/%s * 50) + '%%, transparent ' + (50 + value/%s * 50) + '%%)'",
             max_val,color1,max_val,color1,color2,color2,max_val,max_val))
} 

Using some test data:

data <- data.frame(a=c(rep("a",9)),value=c(-4,-3,-2,-1,0,1,2,3,4))

datatable(data) %>%
  formatStyle('value',
              background=color_from_middle(data$value,'red','blue'))