如何檢查列是否有有效值？

Question

我需要從現有列派生一列後，檢查是否有有效的條目沒有。 INPUT

ID 
    2 

    4 
    6 


    34 

輸出

ID ID_ENTRY 
2 PRESENT 
    NOT PRESENT 
4 PRESENT 
6 PRESENT 
    NOT PRESENT 
    NOT PRESENT 
34 PRESENT 

Answer 1

這裏的一個基礎R選項是使用ifelse：

df$ID_ENTRY <- ifelse(ID != "", "PRESENT", "NOT PRESENT") 

如果你能有空字符串，null或NA遺漏值那麼我們可以使用：

df$ID_ENTRY <- ifelse(ID != "" & !is.na(ID) & !is.null(ID), 
         "PRESENT", "NOT PRESENT") 

Answer 2

通常，這可以用is.na解決：

dat[,"ID_ENTRY"] <- ifelse(is.na(dat[,"ID"]), "NOT PRESENT", "PRESENT") 

但是，有時有必要檢查所討論的列的類型和在這種情況下使用不同的方法。舉例來說，如果它character列，該方法是

dat[, "ID_ENTRY"] <- ifelse(dat[,"ID"]=="", "NOT PRESENT", "PRESENT") 

Answer 3

使用可以使用sapply。

vec1 <- c("a", "b", "c", "") 
vec2 <- sapply(vec1, function(x){ifelse(x == "", "NOT PRESENT", "PRESENT")}) 
vec2 
## "PRESENT"  "PRESENT"  "PRESENT" "NOT PRESENT" 

Answer 4

假設ID是factor

ss <- data.frame(ID = c(2,' ',4,6,' ',' ',34)) 

> ss$ID_ENTRY <- lapply(ss$ID,function(x){ifelse(is.na(as.numeric(as.character(x))),'NOTPRESENT','PRESENT')}) 
> ss 
    ID ID_ENTRY 
1 2 PRESENT 
2 NOTPRESENT 
3 4 PRESENT 
4 6 PRESENT 
5 NOTPRESENT 
6 NOTPRESENT 
7 34 PRESENT 
>