R ggplot with variable inside loop

Question

i have an issue with my ggplot inside my loop. i created a vector with the colnames which i want to loop as a y variable but clearly something is wrong because ggplot function seems to take it as a string and not as a colname in my dataframe.

here is my df :

> head(nbf2020)
  Plant annee rang bloc genotype feuilles9.06 feuilles21.06 feuilles12.07
1    19  2020    A    1    22928           10            16            23
2    20  2020    A    1    25899           12            18            25
3    21  2020    A    1    27819            8            15            25
4    22  2020    A    1    25699           19            24            25
5    23  2020    A    1    24882           11            19            29
6    24  2020    A    1    23948           21            29            39
  feuilles3.08 feuilles19.08 repetition total
1           26            NA          1     5
2           29            NA          1     2
3           31            NA          1     3
4           40            NA          1     2
5           35            NA          1     2
6           45            NA          1     5

i want to create subplot for the col feuilles.XX then i created a vector with the colnames :

> months = colnames(nbf2020[,c(6:10)])
> months
[1] "feuilles9.06"  "feuilles21.06" "feuilles12.07" "feuilles3.08" 
[5] "feuilles19.08"
>

after i used this vector for loop and create ggplot :

for (i in months) {

  y_name = paste("number of leafs counted", i, sep="")
  print(i)
  temp_plot = ggplot(nbf2020, aes(x=bloc, y=i, colour=bloc,fill=bloc))+
  geom_boxplot(outlier.alpha = 0, alpha=0.25)+
  geom_jitter(width=0.25)+  
  stat_summary(fun=mean, colour="black", geom="point", 
               shape=18, size=3) +
  theme_classic()+
  theme(legend.position="none")+
  geom_text(data = myletters_df, aes(label = letter, y = 60 ), colour="black", size=5) + xlab("bloc number") + ylab(y_name) 

  ggsave(temp_plot, file=paste0(i, ".pdf", sep=""), width = 14, height = 10, units = "cm")
}

it's kind of working except that my y value is just the name of the column.

does anyone know what is wrong? thanks for your help !

Maybe I'm missing something, but you are iterating across months, which is a vector of strings, and then you are using that as the y axis value. So it will use the string as the y axis rather than any numeric value. — user438383
– user438383, Commented Sep 19, 2021 at 14:10
I suspect this is a lazy evaluation problem. It usually is when ggplot is used in a for loop. Switch to a member of the apply family (which all force evaluation( and you should be OK. You can get more information on lazy evaluation here. — Limey
– Limey, Commented Sep 19, 2021 at 16:30

Roman Luštrik · Accepted Answer · 2021-09-19 14:09:48Z

2

Since you're using variable i, which turns out to be a string, use aes_string in place of aes.

answered Sep 19, 2021 at 14:09

Roman Luštrik

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2 Comments

Marine Bergot Over a year ago

thanks for your comment, i already tried but i get this error : Error in aes_string(x = bloc, y = i, colour = bloc, fill = bloc) : object 'bloc' not found

Roman Luštrik Over a year ago

Note that all your arguments passed to aes_string need to be characters (that refer to column names in the data.frame).

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