Hello,

We are trying to compute a Kruskal-Wallis test on diversity indices (Chao1, Shannon) through the following code using the function stat_compare_means (that by default uses wilkoxon) from ggpubr.

Code:

my_comparisons <- list(c("gut C. decolorata female","larva"), c("larva","gut C. decolorata male"), c("gut C. decolorata female", "gut C. decolorata male"), c("gut C. decolorata male", "pollen provision"), c("gut C. decolorata female", "pollen provision"), c("larva", "pollen provision"))

p <- plot_richness(physeq, x = "sample_type", measures = c("Chao1", "Shannon"), scales="free_y")


p+ geom_boxplot(aes(fill = sample_type), alpha=0.8)+ guides(fill = guide_legend(title = "Sample type of Centris decolorata and pollen provision"))+
  scale_fill_manual(values = color_cdpp, labels=c("gut C. decolorata female", "gut C. decolorata male", "larva", "pollen provision"))+
  scale_x_discrete(labels=c("gut C. decolorata female", "gut C. decolorata male", "larva", "pollen provision"))+
  xlab("Sample type")+
  theme(axis.title.x =element_text(size=15), axis.title.y =element_text(size=15), axis.text.y = element_text(size=15),
        legend.text = element_text(size=15), 
        strip.text = element_text(size=15),
        legend.title=element_markdown(size=15), axis.text.x = element_text(size=15), 
        legend.justification = "center",
        legend.text.align = 0) -> p1


p1 + stat_compare_means(comparisons = my_comparisons, label="p.signif", method = 'kruskal.test',
                        hide.ns = FALSE,
                        symnum.args = list(cutpoints = c(0, 0.0001, 0.001, 0.01, 0.05, 1), 
                                           symbols = c("*", "*", "", "", "ns")))

We receive the following error:

Warning messages:

1: Computation failed in stat_signif():
'x' and 'g' must have the same length
2: Computation failed in stat_signif():
'x' and 'g' must have the same length

We would greatly appreciate any insight on to why we receive this error message and how we could fix it.