Distinguish the faceting between groups in ggplot2 heatmap

I have this data frame:

gene_symbol<-c("DADA","SDAASD","SADDSD","SDADD","ASDAD","XCVXCVX","EQWESDA","DASDADS","SDASDASD","DADADASD","sdaadfd","DFSD","SADADDAD","SADDADADA","DADSADSASDWQ","SDADASDAD","ASD","DSADD")
panel<-c("growth","growth","growth","growth","big","big","big","small","small","dfgh","DF","DF","DF","DF","DF","gh","DF","DF")
ASDDA<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDb<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf1<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf2<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf3<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf4<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf5<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDA1<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDb1<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf1<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf11<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf21<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf31<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf41<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
ASDDAf51<-c("normal","over","low","over","normal","over","low","over","normal","over","DF","DF","DF","DF","DF","DF","DF","DF")
Gene_states22 <- data.frame(gene_symbol, panel, ASDDA, ASDDb, ASDDAf, ASDDAf1, ASDDAf2, 
                            ASDDAf3, ASDDAf4, ASDDAf5, ASDDA1, ASDDb1, ASDDAf1, ASDDAf11,
                            ASDDAf21, ASDDAf31, ASDDAf41, ASDDAf51)

And I create 6 heatmaps with:

library(plotly)
library(ggplot2); library(reshape2)
HG3 <- split(Gene_states22[,1:15], Gene_states22$panel)
HG4 <- melt(HG3, id.vars= c("gene_symbol","panel"))
HG4 <- HG4[,-5]
HG5 <- split(HG4, HG4$panel)
pp <- ggplot(HG4, 
       aes(gene_symbol,variable)) + 
  geom_tile(aes(fill = value),
            colour = "grey50") + 
  facet_grid(~panel, scales = "free") +

  # it looks like you have more colours than values here.
  # I recommend using a named vector in this case, so that 
  # the same value always maps to the same colour.
  # e.g. values = c("DF" = "white", "low" = "red", ...)
  scale_fill_manual(values = c("white", "red", "blue", "black", "yellow", "green", "brown")) +

  labs(title = "Heatmap", x = "gene_symbol", y = "sample", fill = "value") +
  guides(fill = FALSE)+
  theme(panel.background = element_rect(fill = NA),
        panel.spacing = unit(0, "lines"),
        strip.placement = "outside")

ggplotly(pp,
         width = 1350, height = 600) %>%
  # note: specifying width / height in layout() has been deprecated
  # in recent versions of plotly. when I used it that way, I got
  # a warning to specify it within ggplotly() instead.
  layout(autosize = F, 
         hoverlabel = list(bgcolor = "white",
                           font = list(family = "sans serif", size = 9, color = "black")))

As you can see from the picture below my heatmap is separated into 6 groups. and the name of each group is placed accordingly on this grey zone

I would like somehow to separate this grey zone maybe by 6 different colors instead of only grey or add space between each separated group in order to distinguish better. Of course I would be open to other suggestions.

Solution

You could add more space between each facet. In fact, in your code, you are setting that space to 0, which does not seem to fit your desire.

Try this:

 ggplot(HG4, aes(gene_symbol,variable)) + 
       geom_tile(aes(fill = value),
        colour = "grey50") + 
      facet_grid(~panel, scales = "free") +
      scale_fill_manual(values = c("white", "red", "blue", "black", "yellow", "green", "brown")) +
      labs(title = "Heatmap", x = "gene_symbol", y = "sample", fill = "value") +
      guides(fill = FALSE)+
      theme(panel.background = element_rect(fill = NA),
            panel.spacing = unit(0.5, "lines"), ## It was here where you had a 0 for distance between facets. I replaced it by 0.5 .
            strip.placement = "outside")