令人困惑的行爲價值

Question

確定的載體，這有我絕對感到困惑和worried- 作爲日常工作的一部分，我已經根據被分類的變量個別觀測作爲TRUE或FALSE它們的值是否高於或低於/等於中值。但是，我一直在R中得到一個行爲，這在很大程度上是意外執行這個簡單的測試。

所以借這個組觀察：

data=c(0.6666667, 0.8333, 0.6666667, 0.8333, 0.8333, 0.75, 0.9999, 0.7499667, 0.25, 0.6666667, 0.1667, 0.7499667, 0.5, 0.2500333, 0.3333667, 0.0834, 0.0001, 0.2500333, 0.8333, 0.9999, 0.9999, 0.2500333, 0.2500333, 0.3333667, 0.9166, 0.5, 0.2500333, 0.4166667, 0.0001, 0.1667333, 0.6666333, 0.0834, 0.1667, 0.6666333, 0.9166, 0.1667, 0.7499333, 0.9166, 0.9166, 0.9166, 0.7499667, 0.7499667, 0.4166667, 0.5, 0.2500333, 0.9166, 0.6666667, 0.1667333, 0.25, 0.0001, 0.3333667, 0.0001, 0.25, 0.0834, 0.9999, 0.0834, 0.1667, 0.5, 0.2500333, 0.3333667, 0.9166, 0.9166, 0.8333, 0.9166, 0.75, 0.0834, 0.4166667, 0.5, 0.0001, 0.9999, 0.8333, 0.6666667, 0.9166) 

對我來說，這些值進行分類，我所做的：

data_med=median(data) 
quant_data=data 
quant_data[quant_data>data_med]="High" 
quant_data[quant_data<=data_med]="Low" 

我知道有更有效地這樣做的1點極大數的方式，但什麼我擔心的是，從這個輸出沒有意義。由於有上集中沒有NaN S和測試全包（>或<=），我應該結束了，只有TRUE/FALSE值的列表，而是我得到：

[1] "High" "High" "High" "High" "High" "High" "High" "High" "Low" "High" "Low" "High" "Low" "Low" "Low" "Low" "1e-04" 
[18] "Low" "High" "High" "High" "Low" "Low" "Low" "High" "Low" "Low" "Low" "1e-04" "Low" "High" "Low" "Low" "High" 
[35] "High" "Low" "High" "High" "High" "High" "High" "High" "Low" "Low" "Low" "High" "High" "Low" "Low" "1e-04" "Low" 
[52] "1e-04" "Low" "Low" "High" "Low" "Low" "Low" "Low" "Low" "High" "High" "High" "High" "High" "Low" "Low" "Low" 
[69] "1e-04" "High" "High" "High" "High" 

請參閱「 1E-04" S？更奇怪的，讓我們挑值69，返回奇數值的那些之一：

data[69] 
>1e-04 

如果我單獨測試這個值，我得到了我的預期得到：

data[69]<=data_med 
TRUE 

能

人解釋這種行爲？它看起來完全危險......

Answer 1

讓我們來看看你在這裏做了什麼。

data=c(0.6666667, 0.8333, 0.6666667, 0.8333, 0.8333, 0.75, 0.9999, 0.7499667, 0.25, 0.6666667, 0.1667, 0.7499667, 0.5, 0.2500333, 0.3333667, 0.0834, 0.0001, 0.2500333, 0.8333, 0.9999, 0.9999, 0.2500333, 0.2500333, 0.3333667, 0.9166, 0.5, 0.2500333, 0.4166667, 0.0001, 0.1667333, 0.6666333, 0.0834, 0.1667, 0.6666333, 0.9166, 0.1667, 0.7499333, 0.9166, 0.9166, 0.9166, 0.7499667, 0.7499667, 0.4166667, 0.5, 0.2500333, 0.9166, 0.6666667, 0.1667333, 0.25, 0.0001, 0.3333667, 0.0001, 0.25, 0.0834, 0.9999, 0.0834, 0.1667, 0.5, 0.2500333, 0.3333667, 0.9166, 0.9166, 0.8333, 0.9166, 0.75, 0.0834, 0.4166667, 0.5, 0.0001, 0.9999, 0.8333, 0.6666667, 0.9166) 



data_med=median(data) ## 0.5 
quant_data=data  ## irrelevant 
quant_data[quant_data>data_med]="High" 

但是，這樣做已經轉換quant_data爲一個字符向量：

str(quant_data) 
## chr [1:73] "High" "High" "High" "High" "High" "High" "High" ... 

現在字符值和data_med值之間的比較幾乎是沒有意義的，因爲data_med將得到裹挾一個字符的值也是：

"High" < "0.5" ## FALSE 
"1e-4" < "0.5" ## FALSE -- this is your problem. 
quant_data[quant_data<=data_med]="Low" 

你想的大概是意味着做（和理由分配quant_data=data）是：

quant_data[data>data_med]="High" 
quant_data[data<=data_med]="Low" 
table(quant_data) 
## High Low 
## 35 38 

正如@Arun在上述評論指出，quant_data <- ifelse(data>data_med,"High","Low")將工作太。所以會適當使用cut()。