R-ggplot2等高线图 [英] R - ggplot2 contour plot

问题描述

我正在尝试从R的Coursera上的Andrew Ng的机器学习课程中复制代码（因为该课程在八度中）。

I am trying to replicate the code from Andrew Ng's Machine Learning course on Coursera in R (as the course is in Octave).

基本上，我必须绘制一个多项式正则逻辑回归的非线性决策边界（在p = 0.5时）。

Basically I have to plot a non linear decision boundary (at p = 0.5) for a polynomial regularized logistic regression.

我可以轻松地使用基础库复制图：

I can easily replicate the plot with the base library:

contour(u, v, z, levels = 0)
points(x = data$Test1, y = data$Test2)

其中：

u <- v <- seq(-1, 1.5, length.out = 100)

z是矩阵100x100，其中每个网格点的z值都为z。
数据尺寸为118x3。

and z is a matrix 100x100 with the values of z for every point of the grid. Dimension of data is 118x3.

我无法在ggplot2中做到这一点。有人知道如何在ggplot2中复制吗？我尝试过：

I cannot do it in ggplot2. Does somebody know how to replicate the same in ggplot2? I tried with:

z = as.vector(t(z))
ggplot(data, aes(x = Test1, y = Test2) + geom_contour(aes(x = u, y = 
v, z = z))

但是我得到一个错误：美学必须为长度1或与数据（118）相同：颜色，x，y，形状

But I get the error: Aesthetics must be either length 1 or the same as the data (118): colour, x, y, shape

谢谢。

编辑（添加根据误用代码创建的图）：

EDIT (Adding plot created from code of missuse):

推荐答案

您需要的是将坐标转换为长格式，以下是使用火山数据的示例设置：

What you need is to convert the coordinates into long format. Here is an example using volcano data set:

data(volcano)

$ b在基础R中的
$ b

：

in base R:

contour(volcano)

和ggplot2：

library(tidyverse)
as.data.frame(volcano) %>% #convert the matrix to data frame
  rownames_to_column() %>% #get row coordinates
  gather(key, value, -rowname) %>% #convert to long format
  mutate(key = as.numeric(gsub("V", "", key)), #convert the column names to numbers
         rowname = as.numeric(rowname)) %>%
  ggplot() +
  geom_contour(aes(x = rowname, y = key, z = value))

如果您想像在基础R图中那样直接标记它，可以使用库 directlabels ：

if you would like to label it directly as in base R plot you can use library directlabels:

首先映射颜色/填充到变量：

First map the color/fill to a variable:

as.data.frame(volcano) %>%
  rownames_to_column() %>%
  gather(key, value, -rowname) %>%
  mutate(key = as.numeric(gsub("V", "", key)),
         rowname = as.numeric(rowname)) %>%
  ggplot() +
  geom_contour(aes(x = rowname,
                   y = key,
                   z = value,
                   colour = ..level..)) -> some_plot

然后

library(directlabels)

direct.label(some_plot, list("far.from.others.borders", "calc.boxes", "enlarge.box", 
                     box.color = NA, fill = "transparent", "draw.rects"))

要在特定坐标处添加标记，您只需添加具有适当数据的另一层即可：

to add markers at specific coordinates you just need to add another layer with appropriate data:

上一个情节

as.data.frame(volcano) %>% 
  rownames_to_column() %>% 
  gather(key, value, -rowname) %>% 
  mutate(key = as.numeric(gsub("V", "", key)), 
         rowname = as.numeric(rowname)) %>%
  ggplot() +
  geom_contour(aes(x = rowname, y = key, z = value)) -> plot_cont

添加带有点的图层，例如：

add layer with points for instance:

plot_cont +
  geom_point(data = data.frame(x = c(35, 47, 61),
                               y = c(22, 37, 15)),
             aes(x = x, y = y), color = "red")

您可以通过以下方式添加任何类型的图层： geom_line ， geom_text 仅举几例。

you can add any type of layer this way: geom_line, geom_text to name a few.

EDIT2：要更改轴的比例，有几个选项，一种方法是将适当的行名和姓氏分配给矩阵：

to change the scale of the axis there are several options, one is to assign appropriate rownames and colnames to the matrix:

我将为x轴分配一个从0-2的序列，为y轴分配一个从0-5的序列：

I will assign a sequence from 0 - 2 for the x axis and 0 - 5 to the y axis:

rownames(volcano) <- seq(from = 0,
                         to = 2,
                         length.out = nrow(volcano)) #or some vector like u
colnames(volcano) <- seq(from = 0,
                         to = 5,
                         length.out = ncol(volcano)) #or soem vector like v

as.data.frame(volcano) %>% 
  rownames_to_column() %>% 
  gather(key, value, -rowname) %>% 
  mutate(key = as.numeric(key), 
         rowname = as.numeric(rowname)) %>%
  ggplot() +
  geom_contour(aes(x = rowname, y = key, z = value))

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