Get the strings before the comma with R

问题

I am a beginner with R. Now, I have a vector in a data.frame like this

city
Kirkland,
Bethesda,
Wellington,
La Jolla,
Berkeley,
Costa, Evie KW172NJ
Miami,
Plano,
Sacramento,
Middletown,
Webster,
Houston,
Denver,
Kirkland,
Pinecrest,
Tarzana,
Boulder,
Westfield,
Fair Haven,
Royal Palm Beach, Fl
Westport,
Encino,
Oak Ridge,

I want to clean it. What I want is all the city names before the comma. How can I get the result in R? Thanks!

回答1:

You can use gsub with a bit of regexp :

cities <- gsub("^(.*?),.*", "\\1", df$city)

This one works, too :

cities <- gsub(",.*$", "", df$city)

回答2:

Just for fun, you can use strsplit

> x <- c("London, UK", "Paris, France", "New York, USA")
> sapply(strsplit(x, ","), "[", 1)
[1] "London"   "Paris"    "New York"

回答3:

You could use regexpr to find the position of the first comma in each element and use substr to snip them at this:

x <- c("London, UK", "Paris, France", "New York, USA")

substr(x,1,regexpr(",",x)-1)
[1] "London"   "Paris"    "New York"

回答4:

This works as well:

x <- c("London, UK", "Paris, France", "New York, USA")

library(qdap)
beg2char(x, ",")

## > beg2char(x, ",")
## [1] "London"   "Paris"    "New York"

回答5:

If the this was a column in a dataframe, we can use tidyverse.

library(dplyr)
x <- c("London, UK", "Paris, France", "New York, USA")
x <- as.data.frame(x)
x %>% separate(x, c("A","B"), sep = ',')
        A       B
1   London      UK
2    Paris  France
3 New York     USA

来源：https://stackoverflow.com/questions/19320966/get-the-strings-before-the-comma-with-r