R duplicate rows based on the elements in a string column [duplicate] - r

Question

This question already has answers here:
str_extract_all: return all patterns found in string concatenated as vector
(2 answers)
Closed 2 years ago.
I have a more or less specific question that probably pertains to loops in R. I have a dataframe:
X location year
1 North Dakota, Minnesota, Michigan 2011
2 California, Tennessee 2012
3 Bastrop County (Texas) 2013
4 Dallas (Texas) 2014
5 Shasta (California) 2015
6 California, Oregon, Washington 2011
I have two problems with this data: 1) I need a column that consists of just the state names of each row. I guess this should be generally easy with gsub and using a list of all US state names.
list <- c("Alabama", "Alaska", "Arizona", "Arkansas", "California", "etc")
pat <- paste0("\\b(", paste0(list, collapse="|"), ")\\b")
pat
data$state <- gsub(data$location, "", paragraph)
The bigger issue for me is 2) I need an individual (duplicate) row for each state that is in the dataset. So if row 6 has California, Oregon and Washington in 2011, I need to have a separate row of each one separately like this:
X location year
1 California 2011
2 Oregon 2011
3 Washington 2011
Thank you for your help!

Answer 1

You can use str_extract_all to extract all the states and unnest to duplicate rows such that each state is in a separate row. There is an inbuilt constant state.name which have the state names of US which can be used here to create pattern.
library(dplyr)
pat <- paste0("\\b", state.name, "\\b", collapse = "|")
df %>%
mutate(states = stringr::str_extract_all(location, pat)) %>%
tidyr::unnest(states)
# A tibble: 11 x 3
# location year states
# <chr> <int> <chr>
# 1 North Dakota, Minnesota, Michigan 2011 North Dakota
# 2 North Dakota, Minnesota, Michigan 2011 Minnesota
# 3 North Dakota, Minnesota, Michigan 2011 Michigan
# 4 California, Tennessee 2012 California
# 5 California, Tennessee 2012 Tennessee
# 6 Bastrop County (Texas) 2013 Texas
# 7 Dallas (Texas) 2014 Texas
# 8 Shasta (California) 2015 California
# 9 California, Oregon, Washington 2011 California
#10 California, Oregon, Washington 2011 Oregon
#11 California, Oregon, Washington 2011 Washington
data
df <- structure(list(location = c("North Dakota, Minnesota, Michigan",
"California, Tennessee", "Bastrop County (Texas)", "Dallas (Texas)",
"Shasta (California)", "California, Oregon, Washington"), year = c(2011L,
2012L, 2013L, 2014L, 2015L, 2011L)), class = "data.frame", row.names = c(NA, -6L))