在考试中绘制课程的散点图

Question

我正在尝试绘制一个散点图，显示每个问题为每个学生获得的分数百分比，并计算整个班级的平均值。

maxmarks.paper <- c(4,5,2,4,3,4,5,4,6,3,3,5,3,4,4,4,3,3,2,5,4)

results.student1 <- c(4,3,2,3,3,4,5,4,3,3,0,0,2,4,1,1,2,0,1,0,0)
results.student2 <- c(2,2,0,4,1,1,0,1,4,2,0,0,1,0,0,2,0,0,1,1,0)
#etc.

percentage1 <- results.student1 / maxmarks.paper * 100
percentage2 <- results.student2 / maxmarks.paper * 100
#etc.

我正在查看this教程，但我不明白这是如何工作的。

plot(x = "questions 1:20", y= "percentage of marks gained per student" ...)

有人可以帮助绘制散点图吗？

Answer 1

好的，这里是您的代码以更简洁的方式表达，以及我认为您的要求的情节，但仍然不完全清楚：

maxmarks.paper <- c(4,5,2,4,3,4,5,4,6,3,3,5,3,4,4,4,3,3,2,5,4)

# Input the results as a data frame rather than individual vectors
results <- data.frame(
  student1 = c(4,3,2,3,3,4,5,4,3,3,0,0,2,4,1,1,2,0,1,0,0),
  student2 = c(2,2,0,4,1,1,0,1,4,2,0,0,1,0,0,2,0,0,1,1,0)
)

# Calculate the percentages all at once instead of repeating the equation over and over
percentages <- data.frame(apply(results, 2, function(student) {
  return(student / maxmarks.paper * 100)
}))

# Calculate the class average on each question and store it in the same table
percentages$class_average <- apply(percentages, 1, mean)

# Plot the average mark for each question and label the axes
plot(x = 1:21, y = percentages$class_average, xlab = "Questions 1:21", ylab = "Class Average (%)", pch = 19)

# Add points to the chart for each student
for (i in 1:2) {
  points(x = 1:21, y = percentages[[paste0("student", i)]], col = "green", pch = 19)
}

Answer 2

使用此公式，您可以绘制比较每对学生的散点图，例如

Create application without a manifest

要计算整个班级的平均值，您需要总结每个问题的数据。对于散点图，您只使用两个变量;如果你有20个问题，那么你只能为每对问题做到这一点。

Answer 3

对于每个学生，您似乎正在尝试显示每个问题的百分比标记。您需要在同一图表上绘制多条线。

继续 efbbrown 的回答，（存储results并更有效地计算百分比）。

maxmarks.paper <- c(4, 5, 2, 4, 3, 4, 5, 4, 6, 3, 3, 5, 3, 4, 4, 4, 3, 3, 2, 5, 4)

# Input the results as a data frame rather than individual vectors
results <- data.frame(
  student1 = c(4, 3, 2, 3, 3, 4, 5, 4, 3, 3, 0, 0, 2, 4, 1, 1, 2, 0, 1, 0, 0),
  student2 = c(2, 2, 0, 4, 1, 1, 0, 1, 4, 2, 0, 0, 1, 0, 0, 2, 0, 0, 1, 1, 0)
)

# Calculate the percentages all at once instead of repeating the equation 
over and over
percentages <- data.frame(apply(results, 2, function(student) {
    return(student / maxmarks.paper * 100)
}))

现在绘制图表：

plot (x = 1:21, y = percentages$student1, type = "p", xlab = "Questions in paper", ylab = "Class Average (%)")

type = "p"参数将仅绘制点，添加另一个向量，使用lines函数。

lines(x = 1:21, y = percentages$student2, type = "p", xlab = "Questions in paper", ylab = "Class Average (%)")

您可以为每位学生运行此操作，将他们的百分比添加到图表中。要计算所有学生的平均使用率：

# from efbbrown's answer
percentages$class.average <- apply(percentages, 1, mean)

然后，您可以使用以下方法将其添加到图表中：

lines(x = 1:21, y = percentages$class.average, type = "l", xlab = "Questions in paper", ylab = "Class Average (%)")

type = "l"将仅显示该行，同样type = "o"将同时显示行和点。

以上将如下所示：