RareAir RareAir - 3 months ago 8
R Question

Detect a list of words in a string variable and extract matched words to a new variable in data frame

I have a two variable dataframe one of which is a character vector. Each row in "MyVector" contains a string with exactly one name (i.e. "Pete"). The name can vary in its location in the character string. I want to create code that will match the name in a list with the name in the character string and extract that name into a new variable in the dataframe.
If the name was always in the same position in the vector "MyVector", I would create a new variable as a substring of MyVector pulling out the name into a new column.
I tried various version of str_detect from Stringr to no avail.

Challenge: How do I detect or extract the name into a new variable and place it into MyDF if the name is in multiple positions?

#Create the data frame
var.1 <-rep(c(1,5,3),2)

MyVector <- c("I know Pete", "Jerry has a new job","Victor is an employee","How to work with Pete","Too Many Students","Bob is mean")
MyDF <-as.data.frame(cbind(var.1,MyVector))

#Create a vector of a list of names I want to extract into a new column in the dataframe.
Extract <- c("Jerry","Pete", "Bob", "Victor")

#Match would be perfect if I could use it on character vectors
MyDF$newvar <-match(MyDF$MyVector,Extract)


My final data.frame should look something like the output below.

var.1 MyVector NEWVAR
1 1 Don knows Pete Pete
2 5 Jerry has a new job Jerry
3 3 Victor and Bob are employees Victor
4 1 How to work with Pete Pete
5 5 Too Many Students NA
6 3 Bob is mean Bob

Answer

We can use str_extract after pasteing the 'Extract' together

library(stringr)
MyDF$NEWVAR <- str_extract(MyDF$MyVector, paste(Extract, collapse="|"))
MyDF$NEWVAR
#[1] "Pete"   "Jerry"  "Victor" "Pete"   NA       "Bob"