這是期中考試的進一步分析。除了整體成績的summary外，以 GGplot2 強大的圖形功能來比較大二(2)以及大三以上同學(3+) 期中考成績。

Data Input

exam <- read.delim("~/akno/andy/work/edu/18/i2p/midscore.txt");
colnames(exam)<-c("sid","mid");
attach(exam)
year<-(sid > 410600000)*1
exam$year<- factor(year, levels=c(1,0), labels=c("2", "3+"))
summary(mid); summary(exam$year)
   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
   0.00   25.00   40.00   41.91   58.00  101.00 
 2 3+ 
37 53 
sd(mid)
[1] 23.24836
stem(mid)

  The decimal point is 1 digit(s) to the right of the |

   0 | 00555550003355578
   2 | 0003355589000233333555555
   4 | 000002355780000355555578889
   6 | 0225588000000359
   8 | 0050
  10 | 1

Normality check (plain way)

par(mfrow=c(2,2));    # Setup the graphical device
# I use "mid" as the variable, you can try the command on "final"
hist(mid); boxplot(mid); qqnorm(mid);
plot(density(mid));

Compare and contrast: 2 vs. 3+

library(ggplot2, quietly = T)
RStudio Community is a great place to get help: https://community.rstudio.com/c/tidyverse.
qplot(mid, data = exam, geom = "density", adjust = .6)

qplot(mid, ..density.., data = exam, geom = c("histogram", "density"))

qplot(mid, data = exam, geom = "histogram", fill = year)

qplot(mid, data = exam, geom = "density",
  color = year, adjust = .6)

qplot(mid, ..density.., data = exam, geom = c("histogram", "density"),
  color = year)

qplot(mid, data = exam, facets = year ~ .,
  geom = c("histogram", "density"))

p <- ggplot(exam, aes(year, mid));
p + geom_boxplot(fill = "white", colour = "#3366FF")+ geom_boxplot(outlier.colour = "red", outlier.shape = 1);

# By default, outlier points match the colour of the box. Use
# outlier.colour to override
#p + geom_boxplot(outlier.colour = "red", outlier.shape = 1);
# Boxplots are automatically dodged when any aesthetic is a factor
p + geom_boxplot(aes(colour = year)) + geom_jitter(width = 0.2)

qplot(year, mid, data = exam, geom = c("boxplot", "jitter"),
   fill = year, main = "Midterm Scores by 2 vs. 3+",
   xlab = "Year", ylab = "Scores")

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