R – Defining Your Own Color schemes for HeatMaps

[This article was first published on Doodling with Data, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

This post is intended at those who are beginners at R, and is inspired by a small post in Martin’s bioblog.

First, we plot a “correlation heatmap” using the same logic that Martin uses. In our example, let’s use the Movies dataset that comes with ggplot2.

We take the 6 genre columns, and we can compute the correlation matrix for those 6 columns.
Here’s what the matrix looks like:

> cor(movieGenres) # 6×6 cor matrix
                  Action   Animation      Comedy        Drama
Action       1.000000000 -0.05443315 -0.08288728  0.007760094
Animation   -0.054433153  1.00000000  0.17967294 -0.179155441
Comedy      -0.082887284  0.17967294  1.00000000 -0.255784957
Drama        0.007760094 -0.17915544 -0.25578496  1.000000000
Documentary -0.069487718 -0.05204238 -0.14083580 -0.173443622
Romance     -0.023355368 -0.06637362  0.10986485  0.103545195
            Documentary     Romance
Action      -0.06948772 -0.02335537
Animation   -0.05204238 -0.06637362
Comedy      -0.14083580  0.10986485
Drama       -0.17344362  0.10354520
Documentary  1.00000000 -0.07157792
Romance     -0.07157792  1.00000000

When we plot with the default colors we get:
It is difficult to see the details in the tiles. Now, if you want to better control the colors, you can use the handy colorRampPalette() function and combine that with scale_fill_gradient2.
Let’s say that we want “red” colors for negative correlations and “green” for positives.
(We can gray out the 1 along the diagonal.)

Doing this produces:

If there are values close to 1 or to -1, those will pop out visually. Values close to 0 are a lot more muted.

Hope that helps someone.

References: Using R: Correlation Heatmap with ggplot2

To leave a comment for the author, please follow the link and comment on their blog: Doodling with Data.

R-bloggers.com offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)