將變量傳遞給tidyr的集合以重命名鍵/值列？

Question

我想在自定義函數中調用tidyr::gather()，向其傳遞一對將用於重命名key和value列的字符變量。例如

myFunc <- function(mydata, key.col, val.col) { 
    new.data <- tidyr::gather(data = mydata, key = key.col, value = val.col) 
    return(new.data)  
} 

但是，這不符合要求。

temp.data <- data.frame(day.1 = c(20, 22, 23), day.2 = c(32, 22, 45), day.3 = c(17, 9, 33)) 

# Call my custom function, renaming the key and value columns 
# "day" and "temp", respectively 
long.data <- myFunc(mydata = temp.data, key.col = "day", val.col = "temp") 

# Columns have *not* been renamed as desired 
head(long.data) 
    key.col val.col 
1 day.1  20 
2 day.1  22 
3 day.1  23 
4 day.2  32 
5 day.2  22 
6 day.2  45 

所需的輸出：

head(long.data) 
    day temp 
1 day.1 20 
2 day.1 22 
3 day.1 23 
4 day.2 32 
5 day.2 22 
6 day.2 45 

我的理解是，gather()使用裸變量名稱對於大多數參數（因爲它在這個例子中，使用"key.col"作爲列名作爲反對值存儲在key.col）。我嘗試了很多方法在gather()調用中傳遞值，但大多數返回錯誤。例如，gather()呼叫的myFunc返回Error: Invalid column specification（忽略，爲了說明的目的，該value參數，其具有相同的特性）中的這些三種變體：

gather(data = mydata, key = as.character(key.col) value = val.col) 

gather(data = mydata, key = as.name(key.col) value = val.col) 

gather(data = mydata, key = as.name(as.character(key.col)) value = val.col) 

作爲一種變通方法，我剛重命名呼叫以下的列到gather()：

colnames(long.data)[colnames(long.data) == "key"] <- "day" 

但是考慮gather()的本意是功能重命名的鍵/值列，我怎麼能做到這一點在自定義函數中調用gather()？

Answer 1

爲了把它放在你必須使用gather_()像這樣的功能。

myFunc <- function(mydata, key.col, val.col, gather.cols) { 
    new.data <- gather_(data = mydata, 
         key_col = key.col, 
         value_col = val.col, 
         gather_cols = colnames(mydata)[gather.cols]) 
    return(new.data)  
} 

temp.data <- data.frame(day.1 = c(20, 22, 23), day.2 = c(32, 22, 45), 
day.3 = c(17, 9, 33)) 
temp.data 


    day.1 day.2 day.3 
1 20 32 17 
2 22 22  9 
3 23 45 33 

# Call my custom function, renaming the key and value columns 
# "day" and "temp", respectively 

long.data <- myFunc(mydata = temp.data, key.col = "day", val.col = 
"temp", gather.cols = 1:3) 
# Columns *have* been renamed as desired 
head(long.data) 

    day temp 
1 day.1 20 
2 day.1 22 
3 day.1 23 
4 day.2 32 
5 day.2 22 
6 day.2 45 

如前所述，主要區別在於gather_你必須指定要與gather_cols參數收拾列。

Answer 2

大多數（如果不是全部的話）Haldey使用裸變量名作爲參數的函數（例如dplyr的函數）具有function_版本，它使用常規評估並且「適合用於編程」。所以，你需要什麼應該僅僅是：

myFunc <- function(mydata, key.col, val.col) { 
    tidyr::gather_(data = mydata, key_col = key.col, 
       value_col = val.col, gather_cols = colnames(mydata))   
} 

唯一的「抓」在這裏，它是強制性指定gather_cols，使用gather或可作爲...分開進行時，這是沒有必要的。

然後：

> myFunc2(mydata = temp.data, key.col = "day", val.col = "temp") 
    day temp 
1 day.1 20 
2 day.1 22 
3 day.1 23 
4 day.2 32 
5 day.2 22 
6 day.2 45 
7 day.3 17 
8 day.3 9 
9 day.3 33