CODEWITHSUNDEEP
rdataframeapply
R. Martin
R. Martin

Reputation: 109

apply a function to a subset of a data frame but retain the whole data frame

I have a data frame and a vector identifying the rows I'm interested in:

col1 <- c("June","June","June 11","June 11, 2012","June 14, 2012")
col2 <- c("September", "September", "October 8", "October", "Sept 27, 2012")
monthDF <- data.frame(cbind(col1, col2), stringsAsFactors = FALSE)
v0 <- c(1, 2)

I also have two character vectors I would like to apply to the subset and specific columns.

startMonthV <- paste(c(" 1, ", substr(Sys.Date(), 1, 4)), collapse = "")
endMonthV <- paste(c(" 28, ", substr(Sys.Date(), 1, 4)), collapse = "")

I've tried using variations of the apply() function with paste() being the function I want to use, but to no avail. I would like my final result to be a data frame with all of the rows, but looking like this - the first two rows have been modified with the above startMonthV and endMonthV:

           col1                 col2
1  June 1, 2016   September 28, 2016
2  June 1, 2016   September 28, 2016
3       June 11            October 8
4 June 11, 2012              October
5 June 14, 2012        Sept 27, 2012

I'm new to R, and was wondering if the apply() family would do, or using a function within the plyr package. Any stackoverflow answer I've found either applies to the whole data frame or collapses the data with the aggregate() function.

Thank you.

Upvotes: 3

Views: 188

Answers (1)

akuiper
akuiper

Reputation: 214927

We can use mapply and assign the result back at the corresponding rows:

days <- c("1,", "28,")
monthDF[v0, ] <- mapply(paste, monthDF[v0, ], days, substr(Sys.Date(), 1, 4))
monthDF
           col1               col2
1  June 1, 2016 September 28, 2016
2  June 1, 2016 September 28, 2016
3       June 11          October 8
4 June 11, 2012            October
5 June 14, 2012      Sept 27, 2012

Here we created a vector days according to the specific days you would like to append to the columns.

Upvotes: 1

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