ggplot change fill colour without losing colour gradient - r

Question

Maybe this is a very basic question but I'm a ggplot and R beginner.
I'm using this command to get a barplot:
ggplot(data=melt, aes(x=variable, y=value, fill=value)) +
geom_bar(width=.8, stat="identity") +
xlab("Samples") + ylab("Expression") + ggtitle("Gapdh") +
theme(plot.title=element_text(face="bold", size=12)) +
theme(axis.text.x = element_text(angle = 45, hjust = 1, size=10)) +
theme(axis.text.y = element_text(size=10))
I want to change the colors of barplot, but keeping the gradient of the colors depending on value column. I've tried this but I lose the gradient:
ggplot(data=melt, aes(x=variable, y=value, fill=value)) +
geom_bar(width=.8, stat="identity", fill="red") +
xlab("Samples") + ylab("Expression") + ggtitle("Gapdh") +
theme(plot.title=element_text(face="bold", size=12)) +
theme(axis.text.x = element_text(angle = 45, hjust = 1, size=10)) +
theme(axis.text.y = element_text(size=10))
The data is simple, only two columns( variable - value ):
variable value
1 nu73 13576.49
2 nu73t 10891.88
3 nu81 12673.33
4 nu81t 12159.91
5 nu83 12570.82
6 nu83t 11828.04
Thank you guys in advance

Answer 1

You want to adjust the scale, in particular the continuous scale of fill colors, hence the function scale_fill_continuous().
ggplot(data = melt, aes(x = variable, y = value, fill = value)) +
geom_bar(width = .8, stat = "identity") +
labs(x = "Samples", y = "Expression", title = "Gapdh") +
theme(plot.title = element_text(face = "bold", size = 12),
axis.text.x = element_text(angle = 45, hjust = 1, size = 10),
axis.text.y = element_text(size = 10)) +
scale_fill_continuous(low = "firebrick4", high = "firebrick1")
(I slightly modified your plotting code: you can call theme once with multiple arguments, and I find labs nicer than a bunch of individual labeling calls.)
One other option is to use the palettes from the RColorBrewer package (which are incorporated into ggplot2). The scale_fill_brewer() scale if for discrete color scales, you can "distill" them into continuous scales with scale_fill_distiller(). For example
scale_fill_distiller(type = "seq", palette = "Reds")
To see all of the available scales, run RColorBrewer::display.brewer.all().