如何使用`image`以常规布局显示矩阵？ [英] How to use `image` to display a matrix in its conventional layout?

问题描述

我有一个定义如下的矩阵

I have a matrix defined as follows

dataMatrix <- matrix(rnorm(400), nrow=40)

然后 dataMatix 使用以下方式绘制到屏幕上关注

then dataMatix is plotted to the screen using the following

image(1:10, 1:40, t(dataMatrix)[, nrow(dataMatrix):1])

有人可以解释图像函数的第三个参数是如何工作的吗？我对 [] 内发生的事情感到特别困惑。谢谢

can someone explain how the third argument of the image function works ? I'm particularly confused by what happens inside []. Thanks

推荐答案

没有比说明性的例子更好的了。考虑一个 4 * 2 8个元素的整数矩阵：

There is nothing better than an illustrative example. Consider a 4 * 2 integer matrix of 8 elements:

d <- matrix(1:8, 4)
#     [,1] [,2]
#[1,]    1    5
#[2,]    2    6
#[3,]    3    7
#[4,]    4    8

如果我们 image 这个矩阵与 col = 1：8 ，我们将在颜色和像素之间有一对一的颜色：颜色 i 用于对值 i 的像素进行着色。在R中，颜色可以用0到8的9个整数指定（其中0是白色）。您可以按

If we image this matrix with col = 1:8, we will have a one-to-one map between colour and pixel: colour i is used to shade pixel with value i. In R, colours can be specified with 9 integers from 0 to 8 (where 0 is "white"). You can view non-white values by

barplot(rep.int(1,8), col = 1:8, yaxt = "n")

如果 d 在常规显示中绘制，我们应该会看到以下颜色块：

If d is plotted in conventional display, we should see the following colour blocks:

black  |  cyan
red    |  purple
green  |  yellow
blue   |  gray

---

现在，让我们看看图像将显示：

image(d, main = "default", col = 1:8)

我们期待一个（4行，2列）块显示，但我们得到一个（2行，4列）显示。所以我们想转置 d 然后再试一次：

We expect a (4 row, 2 column) block display, but we get a (2 row, 4 column) display. So we want to transpose d then try again:

td <- t(d)
#     [,1] [,2] [,3] [,4]
#[1,]    1    2    3    4
#[2,]    5    6    7    8

image(td, main = "transpose", col = 1:8)

Em，更好，但似乎行排序是相反的，所以我们想要翻转。实际上，这种翻转应该在 td 的列之间执行，因为 td 有4列：

Em, better, but it seems that the row ordering is reversed, so we want to flip it. In fact, such flipping should be performed between columns of td because there are 4 columns for td:

## reverse the order of columns
image(td[, ncol(td):1], main = "transpose + flip", col = 1:8)

是的，这就是我们想要的！我们现在有一个传统的矩阵显示器。

Yep, this is what we want! We now have a conventional display for matrix.

注意 ncol（td）只是 nrow（d）， td 只是 t（d），所以我们也可写：

Note that ncol(td) is just nrow(d), and td is just t(d), so we may also write:

image(t(d)[, nrow(d):1])

这就是你现在所拥有的。

which is what you have right now.

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