why the order of factor does not change - r

Question

I am trying to make the order from small to big when I plot a figure .
This is the data
df <- structure(list(label = structure(c(1L, 1L, 2L, 2L, 3L, 3L, 4L,
4L, 5L, 5L, 6L, 6L), .Label = c(" data1", " data10", " data15",
" data20", " data5", " data8"), class = "factor"), variable = structure(c(1L,
2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L), .Label = c("boys",
"girls"), class = "factor"), N = structure(c(1L, 1L, 2L, 2L,
3L, 3L, 4L, 4L, 5L, 5L, 6L, 6L), .Label = c("1", "10", "15",
"20", "5", "8"), class = "factor"), value = c(93987048.3466667,
54815262.22, 2050259639.66667, 2154175512.5, 3101847435.66667,
2881192196, 6625604632, 3739286226.5, 270853386.15, 430516498,
675222758.633333, 717219589.4), sd = c(129474855.769856, 48756976.8630242,
777498079.458271, 301433971.74375, 1109031077.05936, 45164769.8052193,
1060915464.90521, 1147931493.65351, 239740705.411582, 38453433.9415797,
123930253.814345, 112112765.581137), se = c(74752342.8320143,
34476388.97, 448888725.46965, 213146005.5, 640299390.87988, 31936315,
612519829.250459, 811710143.5, 138414360.805088, 27190683.9,
71551165.4004505, 79275696.8), ci = c(321633371.941334, 438064056.816815,
1931412299.99575, 2708276784.58082, 2754985922.02623, 405789356.908967,
2635460115.35016, 10313755269.7407, 595548927.354538, 345490396.550009,
307859817.127003, 1007293234.14371)), .Names = c("label", "variable",
"N", "value", "sd", "se", "ci"), row.names = c(NA, -12L), class = "data.frame")
based on this answer, I should be able to convert the label to character and then factor and then sort it. How do you specifically order ggplot2 x axis instead of alphabetical order?
So I did like this
df$N <- as.character(df$N)
#Then turn it back into an ordered factor
df$N <- factor(df$N, levels=unique(df$N))
If I str the df, I can see that it change the character to factor but the level does not change
I even tried to manually change the level
df$N <- factor(df$N, levels=c("1","5","8","10","15","20"))
but I am still unable to change the order in plot
so if i do df[order(df$N),] nothing happens
library(ggplot2)
pd <- position_dodge(0.1)
ggplot(df, aes(x=N, y=value, colour=variable)) +
geom_errorbar(aes(ymin=value-se, ymax=value+se), width=.1, position=pd) +
geom_line(position=pd) +
geom_point(position=pd)

Answer 1

Convert N to character then to numeric and sort it.
# Sort N (Using OPs data)
df$N2 <- factor(df$N, levels = sort(unique(as.numeric(as.character(df$N)))))
library(ggplot2)
ggplot(df, aes(N2, value, colour = variable)) +
geom_errorbar(aes(ymin = value - se, ymax = value + se),
width = 0.1, position = pd) +
geom_line(position = pd) +
geom_point(position = pd)

Answer 2

So it seems that there's a distinction between the problem you're proposing, and the question you linked to. In the question linked, they were using X, Y, and Z as representations of groups. They wanted those groups ordered in a specific way.
Here, you are using numbers, and you want them in ascending order. You shouldn't categorize them as factor. Rather, they should be categorized as numeric.
You may still load your numeric data in as a factor, but you'll need to convert it to character first, and then numeric.
df$N <- as.numeric(as.character(df$N))
pd <- position_dodge(0.1)
ggplot(df, aes(x=N, y=value, colour=variable)) +
geom_errorbar(aes(ymin=value-se, ymax=value+se), width=.1, position=pd) +
geom_line(position=pd) +
geom_point(position=pd)