CODEWITHSUNDEEP
rdataframe
pheeper
pheeper

Reputation: 1527

Split string in data frame into two columns

In R I've converted a DocumentTermMatrix with an ngram of 4 into a dataframe and now I want to split the ngram into two columns, one with the first 3 words of the string, the other with the last word. I can accomplish this through multiple steps, however given the size of the df I was hoping to get it accomplished in on line.

Here's what I'm trying to accomplish:

#             str_name           w123   w4 freq
# 1 One Two Three Four One Two Three  Four   10

This gives me the first three words:

df <- data.frame(str_name = "One Two Three Four", freq = 10)
df %>% separate(str_name, c("w123","w4"), sep = "\\w+$", remove=FALSE)

#             str_name           w123 w4 freq
# 1 One Two Three Four One Two Three       10

This gives me the last word but also contains a space:

df <- data.frame(str_name = "One Two Three Four", freq = 10)
df %>% separate(str_name, c("sp","w4"), sep = "\\w+\\s\\w+\\s\\w+", remove=FALSE)

#             str_name sp    w4 freq
# 1 One Two Three Four     Four   10

This is the long way

df <- data.frame(w4 = "One Two Three Four", freq = 10)
df <- df %>% separate(w4, c('w1', 'w2', 'w3', 'w4'), " ")
df$lookup <- paste(df$w1,df$w2,df$w3)

#      w1    w2    w3       w4 freq        lookup
# 1   One   Two Three     Four   10 One Two Three

Upvotes: 1

Views: 474

Answers (2)

akrun
akrun

Reputation: 887731

We can use base R methods to solve this

res <- cbind(df, read.table(text=sub("\\s(\\S+)$", ",\\1", df$str_name), 
  sep=",", header=FALSE, col.names = c("w123", "w4"), stringsAsFactors=FALSE))[c(1,3,4,2)]
res
#            str_name          w123   w4 freq
#1 One Two Three Four One Two Three Four   10

Upvotes: 0

akuiper
akuiper

Reputation: 215117

Try \\s(?=\\w+$) which looks for the space before the last word in the string to split:

df %>% separate(str_name, into = c("w123", "w4"), sep = "\\s(?=\\w+$)", remove = F)
#             str_name          w123   w4 freq
# 1 One Two Three Four One Two Three Four   10

\\s(?=[\\S]+$) is another option which is more greedy than the above one which looks for the last space in the string to split.

df %>% separate(str_name, into = c("w123", "w4"), sep = "\\s(?=[\\S]+$)", remove = F)
#             str_name          w123   w4 freq
# 1 One Two Three Four One Two Three Four   10

Upvotes: 4

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