how to use xticks in Gadfly spy function

Question

I'm using spy function from Gadfly package to plot a heatmap or a matrix of values.

and i want to show for each column a specific string but i cannot find the correct syntax

plt = Gadfly.spy(mtx, x= ["a","b","c","d"])  #suppose mtx has 4 columns

thanks!

Answer 1

Per the original request

using Gadfly

parameters = ["ξ₁", "η₁",  "ξ₂", "η₂"]
spy(rand(4,4), Scale.y_discrete(labels = i->parameters[i]), Scale.x_discrete, 
    Guide.ylabel("Parameters"), Guide.xlabel("Mode"))