爲什麼我只能從R中的cor（）函數中獲取1和-1？

Question

我正在嘗試執行與cor（）函數的Pearson相關性，但輸出結果只給出了1和-1，而不是係數本身。所以當我用corrplot（）繪製矩陣時，我只能看到那些1和-1值。我該如何解決？ 我的數據集可以發現here，看看我的腳本樓下：

##Must load the libraries we will need! IF you have not installed the packages, do that before you start. 
library("corrplot") 
##Load in your datasets 
D1=BPT5test 
##if you don't have a Y (i.e, you want the same thing to be in both axis), leave this blank 
D2= 
##Run the spearman correlation. If you want to do a Pearson, change "spearman to "pearson" 
##If you have 0s in your dataset, set use = "complete.obs", if you have no 0s, set use = "everything" 
CorTest=cor(D1, use = "everything", method = "pearson") 
##Let's get to plotting! 
##Lots of changing you can do! 
#Method can be "circle" "square" "pie" "color" 
#ColorRampPalette can be changed, "blue" being the negative, "White" being '0', and "red" being the positive 
#Change the title to whatever you want it to be 
#tl.col is the color of your labels, this can be set to anything.. default is red 
CorGraph=corrplot(CorTest, method = "circle", col = colorRampPalette(c("blue","white","red"))(200), title = "Pearson's Correlation of High-Fat Sugar at 8 weeks", tl.cex = .5, tl.col = "Black",diag = TRUE, cl.ratio = 0.2) 

Answer 1

您的數據集包含每個變量只有2個觀察值。任何兩個由只有兩個觀察值組成的變量之間的相關性始終爲-1或1.要親眼看看，請嘗試運行replicate(1e2, cor(rnorm(2), rnorm(2)))，其中計算兩個觀察值組成的兩個變量之間的100個相關性。結果始終是-1或1.

Answer 2

這是因爲你只有兩個柱意見。

test <- data.frame(a=c(1,2),b=c(2,3),c=c(4,-2)) 
cor(test, use = "everything", method = "pearson") 
    a b c 
a 1 1 -1 
b 1 1 -1 
c -1 -1 1 

您不能指望只有兩個值的不同輸出，請檢查Pearson correlation formula。

由於三個或更多，你將有更多的變化：

test <- data.frame(a=c(1,2,3),b=c(2,3,5),c=c(4,-2,-10)) 
cor(test, use = "everything", method = "pearson") 
      a   b   c 
a 1.0000000 0.9819805 -0.9966159 
b 0.9819805 1.0000000 -0.9941916 
c -0.9966159 -0.9941916 1.0000000