R-应用基于逻辑向量的函数

Question

I have the following code, but it throws the following error:

the condition has length > 1 and only the first element will be used

Obviously this means that I am misusing the if (condition) {action} construction, so I'm looking for a more elegant way to do this:

if (grepl("Spring", data$Survey)) {data["Season"] <- "Spring"}
if (grepl("Summer", data$Survey)) {data["Season"] <- "Summer"}
if (grepl("Fall", data$Survey)) {data["Season"] <- "Fall"}

Basically, I would like to input a logical vector, and for every TRUE , apply a function to a data set of the same length (in this case, assigning a string value to that row of a dataframe).

Answer 1

You could do this in one step using eg stringr::str_extract . It will return <NA> if there is no match.

library(dplyr)
library(stringr)

data <- data.frame(Survey = sample(c("it's Spring yay",
                                     "it's Summer yay",
                                     "it's Fall yay"),
                            20, replace = TRUE))

data <- data %>% 
  mutate(Season = str_extract(Survey, "(Spring|Summer|Fall)"))

Answer 2

You can use ifelse which is vectorial instead of if :

data$Season <- ifelse(grepl("Spring", data$Survey), 
                         "Spring", 
                         ifelse(grepl("Summer", data$Survey), 
                                "Summer",  
                                ifelse(grepl("Fall", data$Survey), 
                                       "Fall",
                                       "Winter")))

For each element of data$Survey : First ifelse will check if it contains "Spring" , then assign it to the corresponding item in data$Season , otherwise second ifelse will check if it contains "Summer"...

Answer 3

We can use base R to do this

data$Season <-  regmatches(data$Survey, regexpr("\\b(Spring|Survey|Fall)\\b", data$Survey))
data$Season
#[1] "Spring" "Spring" "Fall"   "Fall"   "Spring" "Spring" "Fall"   "Spring" "Fall"   "Spring" "Spring"
#[12] "Fall"   "Spring" "Fall"  

data

data <- data.frame(Survey = sample(c("it's Spring yay",
                                 "it's Summer yay",
                                 "it's Fall yay"),
                        20, replace = TRUE))