Kevin Yang Kevin Yang - 24 days ago 6
R Question

ggplot2 Multiple continuous variable plotting

I have a dataset that looks like this:

Distance Mean SD Median VI Vegetation.Index Direction X X.1 X.2 X.3
1 10m 0.525 0.082 0.530 NDVI NDVI Whole Landscape NA NA NA NA
2 25m 0.517 0.085 0.523 NDVI NDVI Whole Landscape NA NA NA NA
3 50m 0.509 0.086 0.514 NDVI NDVI Whole Landscape NA NA NA NA
4 100m 0.494 0.090 0.497 NDVI NDVI Whole Landscape NA NA NA NA
5 10m 0.545 0.076 0.551 NDVIe NDVI East NA NA NA NA
6 25m 0.542 0.078 0.549 NDVIe NDVI East NA NA NA NA


> dput(droplevels(head(data)))
structure(list(Distance = structure(c(2L, 3L, 4L, 1L, 2L, 3L), .Label = c("100m",
"10m", "25m", "50m"), class = "factor"), Mean = c(0.525, 0.517,
0.509, 0.494, 0.545, 0.542), SD = c(0.082, 0.085, 0.086, 0.09,
0.076, 0.078), Median = c(0.53, 0.523, 0.514, 0.497, 0.551, 0.549
), VI = structure(c(1L, 1L, 1L, 1L, 2L, 2L), .Label = c("NDVI",
"NDVIe"), class = "factor"), Vegetation.Index = structure(c(1L,
1L, 1L, 1L, 1L, 1L), .Label = "NDVI", class = "factor"), Direction = structure(c(2L,
2L, 2L, 2L, 1L, 1L), .Label = c("East", "Whole Landscape"), class = "factor"),
X = c(NA, NA, NA, NA, NA, NA), X.1 = c(NA, NA, NA, NA, NA,
NA), X.2 = c(NA, NA, NA, NA, NA, NA), X.3 = c(NA, NA, NA,
NA, NA, NA)), .Names = c("Distance", "Mean", "SD", "Median",
"VI", "Vegetation.Index", "Direction", "X", "X.1", "X.2", "X.3"
), row.names = c(NA, 6L), class = "data.frame")


I would like to create a barplot facet grid with a categorical variable on the x-axis (Distance), continuous variable on the y-axis (vegetation index) and two bars (mean and median vegeation index values) for each barplot. The bar plots facet by 'Direction' and 'Vegetation Index'.

I have done this with one type of measure (mean), pictured below.

output

Here is the code I have now:

p = ggplot(data,aes(x=Distance,y=Mean,fill=Distance)) + geom_bar(stat =
'identity',position='dodge')+ facet_grid(Direction~Vegetation.Index)+
coord_cartesian(ylim=c(0.2,0.95)) + geom_errorbar(data = data,
aes(ymin=Mean-SD,ymax=Mean+SD),width=0.5)


But I also want a bar for median beside it.

Like this but for all the bar plots in the facet grid.

I found some threads of people wanting to do this exact or similar thing, and found them to be fairly useful:

This

Or this

However, my data looks very different from theirs (I think) and changing it in any way messes up what I already have. From what I understand I have to use group='Mean+Median'.

Answer

Using your sample data, we first convert it to long format. I use tidyr::gather here, but reshape2::melt (or data.table::melt) work similarly.

library(tidyr)
dfl = gather(df, key = measure, value = value, Mean, Median)

dodge_width = 0.8
ggplot(dfl,
       aes(x = measure, y = value, fill = Distance, group = Distance)) +
    geom_bar(stat = 'identity',
             position = position_dodge(dodge_width),
             width = dodge_width) +
    facet_grid(Direction ~ Vegetation.Index) + 
    coord_cartesian(ylim = c(0.2, 0.95)) + 
    geom_errorbar(
        aes(ymin = value - SD, ymax = value + SD),
        width=0.5,
        position = position_dodge(dodge_width)
    )

enter image description here