Zastąp pierwsze wystąpienie ":", ale nie drugie w R

Question

Aby móc przetworzyć chciałbym zastąpić pierwsze wystąpienie : w ciągu znaków (co jest moim znacznikiem, że zaczyna się mowa).

text <- c("Mr. Mark Francois (Rayleigh) (Con): If the scheme was so poorly targeted, why were the Government about to roll it out to employees in the Department of Trade and Industry and the Department for Work and Pensions on the very day the Treasury scrapped it? The CBI and the TUC have endorsed the scheme, which has helped 500,000 people and their families to improve their computer skills. When the Chancellor announced the original concession, he told the Daily Record:", "Even at this eleventh hour, will the Government recognise that this is a poor decision, taken by an analogue Chancellor who is stuck in the past and reversing?", "Dawn Primarolo: The hon. Gentleman answers his own question, as the US does not have similar schemes. He is right to address the question of how we give people in the greatest need access to computer technology, but the Low Pay Commission\u0092s 2005 report showed that that was not happening under the scheme. Why should the Government spend £200 million on a poorly targeted scheme? It was being abused and was not delivering, so the Government have refocused to ensure that the objective is achieved.") 

jestem w stanie znaleźć pozycję pierwszego : użyciu

lapply(gregexpr("\\:", text), head, 1) 

[[1]] 
[1] 35 

[[2]] 
[1] -1 

[[3]] 
[1] 15 

Jestem jednak w stanie zastąpić go w text (powiedzmy, na przykład, z |).

Answer 1

Możemy użyć sub, ponieważ dopasowuje tylko pierwsze wystąpienie wzorca :, a następnie zamieniamy go na |.

sub(':', '|', text) 

Answer 2

Można również użyć str_replace z stringr opakowaniu.

text1 <- c("ABC:DEF:", "SDF", "::ASW") 
library(stringr) 
str_replace(text1, ":", "|") 
# [1] "ABC|DEF:" "SDF"  "|:ASW" 

ta zastępuje pierwsze wystąpienie : z |.