How make a gradient plot in R from a matrix data stored in a .csv file?

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I have a xyz matrix stored in a .csv file that, for example, looks like the following:

   1  2  3  4
1  1  1 -1  1
2 -1  1  1  1
3  1 -1  1 -1
4  1  1 -1  1

where the rows are x, columns are y and entries are z. I could store this matrix in a dataframe.

I want to create a heatmap of this matrix, where the entries would just be two colors, depending on 1 or -1. The plot would look like the following for an 18 X 18 matrix (done by a colleague in matlab probably):

where, say, yellow is for 1 and blue for -1.

How can I do this in R?

heatmap csv r matrix
2 Answers

Use geom_tile(). First you need to flatten your dataframe using melt from the package reshape2.

library(reshape2)
flat_df <- melt(t(df), value.name = "Value")
ggplot(data=flat_df,aes(y=y,x=x))+geom_tile(aes(fill=Value))+scale_y_reverse()

Output from above code

user_195232670

Multiple ways, but a base way is to use image(). Starting with a matrix:

# Matrix needs to be rotated 90 degrees before plotting with image()
m <- t(m[nrow(m):1, ])
image(m, axes = FALSE, col = c("navyblue", "yellow"))
axis(2, at = seq(0, 1, length.out = nrow(m)), labels = rev(seq(nrow(m))), las = 1, tcl = 0.5)
axis(1, at = seq(0, 1, length.out = ncol(m)), labels = seq(ncol(m)), tcl = 0.5)
box()

enter image description here

Data:

txt <- "1  1 -1  1
-1  1  1  1
1 -1  1 -1
1  1 -1  1"

m <- matrix(scan(text = txt, quiet = TRUE), byrow = TRUE, nrow = 4, dimnames =  list(1:4, 1:4))
user_28352610
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