[R] Make barplot with error bars, anova out of a table

[Simza]

Helo everybody,
I'm new to R and have some issues with my data in R. 

My raw data look like that:

ID Day size 1 1 7 1 1 7.2 1 1 7.1 2 1 7.3 2 1 7.4 2 1 7.2 3 1 7 3 1 7.1 3 1
7.5 4 1 7.3 4 1 7.2 4 1 7.6 1 2 7 1 2 7.2 1 2 7.1 2 2 7.1 2 2 7.4 2 2 7.2 3
2 7.5 3 2 7.1 3 2 7.5 4 2 7.2 4 2 7.2 4 2 7.3 1 3 7.4 1 3 7.2 1 3 7.1 2 3
7.2 2 3 7.4 2 3 7.2 3 3 7.4 3 3 7.2 3 3 7.5 4 3 7.4 4 3 7.2 4 3 7.7

What I want to do is:
1) calculate the significant difference of the size for the 4 groups but
each day separately!)? E.g. difference in size between ID 1:2, 1:3, 1:4,
2:3, 2:4, 3:4 for each day.

I already tried lm() and anova() but just get the difference between day, ID
and size. I also tried to separate the data per hand but I think there
should be a way in "R" to do that automatically!? Moreover, I was searching
the web for similar examples but couln't find anything useful so far.

2) to make a barplot with error bars of the standart error (from the mean).
So far I used: 
barplot(matrix(c(Rtest.dat$pH.mean),nr=3), beside=T,
col=c("black","grey","white"), main="pH", names.arg=c("Green", "Yellow",
"Blue", "Red"), ylab="pH") legend("topright", c("Day 1","Day 2","Day 3"),
cex=0.6, bty="n", fill=c("black","grey","white"))
But I have problems to add the error bars. Also here I already searched the
web but couldn't manage to get a code working for my data.

3) and the last thing I would need is to add * or letters (a,b,...) to the
graph, indicating the significant difference between them.

Hope someone can help me!

Thanks for your help!!



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