Search code examples
rggplot2geom-bar

ggplot2 geom_bar - how to keep order of data.frame

I have a question concerning the order of data in my geom_bar.

This is my dataset: 

  SM_P,Spotted melanosis on palm,16.2
  DM_P,Diffuse melanosis on palm,78.6
  SM_T,Spotted melanosis on trunk,57.3
  DM_T,Diffuse melanosis on trunk,20.6
  LEU_M,Leuco melanosis,17
  WB_M,Whole body melanosis,8.4
  SK_P,Spotted keratosis on palm,35.4
  DK_P,Diffuse keratosis on palm,23.5
  SK_S,Spotted keratosis on sole,66
  DK_S,Diffuse keratosis on sole,52.8
  CH_BRON,Dorsal keratosis,39
  LIV_EN,Chronic bronchities,6
  DOR,Liver enlargement,2.4
  CARCI,Carcinoma,1

I assign the following colnames:

  colnames(df) <- c("abbr", "derma", "prevalence") # Assign row and column names

Then I plot:

  ggplot(data=df, aes(x=derma, y=prevalence)) + geom_bar(stat="identity") + coord_flip()

Plot

Why does ggplot2 randomly change the order of my data. I would like to have the order of my data in align with my data.frame.

Any help is much appreciated!

Solution

  • Posting as answer because comment thread getting long. You have to specify the order by using the factor levels of the variable you map with aes(x=...)

    # lock in factor level order
df$derma <- factor(df$derma, levels = df$derma)

# plot
ggplot(data=df, aes(x=derma, y=prevalence)) + 
    geom_bar(stat="identity") + coord_flip()

    Result, same order as in df: enter image description here

    # or, order by prevalence:
df$derma <- factor(df$derma, levels = df$derma[order(df$prevalence)])

    Same plot command gives:

    enter image description here

    I read in the data like this:

    read.table(text=
"SM_P,Spotted melanosis on palm,16.2
DM_P,Diffuse melanosis on palm,78.6
SM_T,Spotted melanosis on trunk,57.3
DM_T,Diffuse melanosis on trunk,20.6
LEU_M,Leuco melanosis,17
WB_M,Whole body melanosis,8.4
SK_P,Spotted keratosis on palm,35.4
DK_P,Diffuse keratosis on palm,23.5
SK_S,Spotted keratosis on sole,66
DK_S,Diffuse keratosis on sole,52.8
CH_BRON,Dorsal keratosis,39
LIV_EN,Chronic bronchities,6
DOR,Liver enlargement,2.4
CARCI,Carcinoma,1", header=F, sep=',')
colnames(df) <- c("abbr", "derma", "prevalence") # Assign row and column names