conditional concatenation in R - r

Question

I have a vector like this:
> myarray
[1] "AA\tThis is ",
[2] "\tthe ",
[3] "\tbegining."
[4] "BB\tA string of "
[5] "\tcharacters."
[6] "CC\tA short line."
[7] "DD\tThe "
[8] "\tend."`
I am trying to write a function that processes the above to generate this:
> myoutput
[1] "AA\tThis is the begining."
[2] "BB\tA string of characters."
[3] "CC\tA short line"
[4] "DD\tThe end."`
This is doable by looping through the rows and using an if statement to concatenate the current row with the last one if it starts with a \t. I was wondering if there is a more efficient way of achieving the same result.

Answer 1

# Create your example data
myarray <- c("AA\this is ", "\tthe ", "\tbeginning", "BB\tA string of ", "\tcharacters.", "CC\tA short line.", "DD\tThe", "\tend")
# Find where each "sentence" starts based on detecting
# that the first character isn't \t
starts <- grepl("^[^\t]", myarray)
# Create a grouping variable
id <- cumsum(starts)
# Remove the leading \t as that seems like what your example output wants
tmp <- sub("^\t", "", myarray)
# split into groups and paste the groups together
sapply(split(tmp, id), paste, collapse = "")
And running it we get
> sapply(split(tmp, id), paste, collapse = "")
1 2
"AA\this is the beginning" "BB\tA string of characters."
3 4
"CC\tA short line." "DD\tThe end"

Answer 2

An option is to use paste than replace AA,BB etc. with additional character say ## and and strsplit as:
#Data
myarray <- c("AA\this is ", "\tthe ", "\tbeginning", "BB\tA string of ",
"\tcharacters.", "CC\tA short line.", "DD\tThe", "\tend")
strsplit(gsub("([A-Z]{2})","##\\1",
paste(sub("^\t","", myarray), collapse = "")),"##")[[1]][-1]
# [1] "AA\this is the beginning"
# [2] "BB\tA string of characters."
# [3] "CC\tA short line."
# [4] "DD\tTheend"