Changing the default properties of geom_line, geom_point, etc.

[John Harrold]

Hello,

This may be a very naive question as I'm very new to R and ggplot. I know that I can specify properties each time I add a layer using geom_line for example below:

x = seq(0,10, by=.1)

y1 = sin(x)

y2 = cos(x)

myd = data.frame(x =x, y1=y1, y2=y2)

p = ggplot()

p = p + geom_line(data=myd, aes(x=x, y=y1), color='blue', size=2) 

p = p + geom_line(data=myd, aes(x=x, y=y2), color='red', size=2) 

print(p)

What is the appropriate way to change (for example) the default size of lines so I do not have to specify it for each layer?

Thanks

John

[Doug Mitarotonda]

Hi John,

ggplot usually thinks of the input as “long” data frames, not “wide.” See packages `tidyr` and `reshape2` for more information on how to use tools to convert. But just using your example the way I would do it is:

# same

x = seq(0,10, by=.1)

y1 = sin(x)

y2 = cos(x)

# I am manually creating the long version, but could be done using `tidyr` or `reshape2`

myd2 <- data.frame(x = c(x, x), y = c(y1, y2), type = c(rep("y1", length(y1), rep("y2", length(y2)))), stringsAsFactors = FALSE)

# Note how you “map” the type on to the color aesthetic

p <- ggplot(myd2, aes(x = x, y = y)) + geom_line(aes(color = type), size = 2)

# if you want to manually set the colors of the lines

p <- p + scale_color_manual(values = c("blue", "red"))

print(p)

Cheers,

Doug

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[Roman Luštrik]

In addition to Doug's comments, here is how I would melt your data.frame and use a RColorBrewer palette.

library(reshape2)

head(myd)

molten.xyd <- melt(myd, id.vars = "x")

ggplot(molten.xyd, aes(x = x, y = value, color = variable)) +

    theme_bw() +

    scale_color_brewer(palette = "Set1") +

    geom_line()

--

In God we trust, all others bring data.

[John Harrold]

I apologize, I don't think I was clear. What I wanted was the appropriate way to change the default line thickness for all lines instead of specifying it each time I called geom_line(). Similarly how would I change the default size of points using geom_point(). I would imagine these are done using theme(), but I'm not sure how to go about changing the defaults.

Sorry again if I wasn't clear.