[R] facet_wrap(nrow) ignored

[Ulrik Stervbo]

Dear Ivan,

I don't think it is possible to force a number of rows - but I'm 
honestly just guessing.

What you can do is to add an empty plot. Here I use cowplot, but 
gridExtra should also work well.

I add an indication of the row number for the plot to the initial 
data.frame, and loop over these.

In the first variant, I add an unused factor to the grp which creates an 
empty facet. I personally think this looks a little confusing, so in the 
second variant, I add a number of empty plots.

HTH
Ulrik

```
mydf <- data.frame(
   grp = rep(letters[1:6], each = 15),
   cat = rep(1:3, 30),
   var = rnorm(90),
   row_num = rep(c(1, 1, 2, 3, 4, 5), each = 15)
)

s_mydf <- split(mydf, mydf$row_num)

plots_mydf <- lapply(s_mydf, function(x){
   # Ensure no unused factors
   x$grp <- droplevels.factor(x$grp)
   if(length(unique(x$grp)) == 1){
     x$grp <- factor(x$grp, levels = c(unique(x$grp), ""))
   }
   ggplot(data = x, aes(x = cat, y = var)) + geom_point() +
     facet_wrap(~grp, drop=FALSE)
})

cowplot::plot_grid(plotlist = plots_mydf, nrow = 5)

# Maybe more elegant output
plots_mydf <- lapply(s_mydf, function(x, ncol = 2){
   # Ensure no unused factors
   x$grp <- droplevels.factor(x$grp)
   x <- split(x, x$grp)

   p <- lapply(x, function(x){
     ggplot(data = x, aes(x = cat, y = var)) + geom_point() +
       facet_wrap(~grp)
   })

   if(length(p) < ncol){
     pe <- rep(list(ggplot() + theme_void()), ncol - length(p))
     p <- c(p, pe)
   }
   cowplot::plot_grid(plotlist = p, ncol = ncol)
})

cowplot::plot_grid(plotlist = plots_mydf, ncol = 1)

# Or if you prefer not to split the plots on the same row
plots_mydf <- lapply(s_mydf, function(x, ncol = 2){

   p <- list(ggplot(data = x, aes(x = cat, y = var)) + geom_point() +
     facet_wrap(~grp))

   if(length(unique(x$grp)) < ncol){
     pe <- rep(list(ggplot() + theme_void()), ncol - length(p))
     p <- c(p, pe)
   }else{
     ncol <- 1
   }
   cowplot::plot_grid(plotlist = p, ncol = ncol)
})

cowplot::plot_grid(plotlist = plots_mydf, ncol = 1)

```

On 2020-09-09 17:30, Ivan Calandra wrote:
> Dear useRs,
> 
> I have an issue with the argument nrow of ggplot2::facet_wrap().
> 
> Let's consider some sample data:
> mydf <- data.frame(grp = rep(letters[1:6], each = 15), cat = rep(1:3,
> 30), var = rnorm(90))
> 
> And let's try to plot with 5 rows:
> library(ggplot2)
> ggplot(data = mydf, aes(x = cat, y = var)) + geom_point() +
> facet_wrap(~grp, nrow = 5)
> It plots 2 rows and 3 columns rather than 5 rows and 2 columns as 
> wanted.
> 
> These plots are as expected:
> ggplot(data = mydf, aes(x = cat, y = var)) + geom_point() +
> facet_wrap(~grp, nrow = 2)
> ggplot(data = mydf, aes(x = cat, y = var)) + geom_point() +
> facet_wrap(~grp, nrow = 6)
> 
> My guess is that 5 rows is not ideal for 6 facets (5 facets in 1st
> column and only 1 facet for 2nd column) so it overrides the value of
> nrow. In the case of 2 or 6 rows, the facets are well distributed in 
> the
> layout.
> 
> The reason why I need 5 rows with 6 facets is that this facet plot is
> part of a patchwork and I would like to have the same number of rows 
> for
> all facet plots of the patchwork (so that they all align well).
> 
> Is there a way to force the number of rows in the facet_wrap()?
> 
> Thank you in advance.
> Best,
> Ivan
> 
> --
> 
> 
> --
> Dr. Ivan Calandra
> TraCEr, laboratory for Traceology and Controlled Experiments
> MONREPOS Archaeological Research Centre and
> Museum for Human Behavioural Evolution
> Schloss Monrepos
> 56567 Neuwied, Germany
> +49 (0) 2631 9772-243
> https://www.researchgate.net/profile/Ivan_Calandra
> 
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