CODEWITHSUNDEEP
rdataframe
user3860074
user3860074

Reputation: 171

Cumulatively paste (concatenate) values grouped by another variable

I have a problem dealing with a data frame in R. I would like to paste the contents of cells in different rows together based on the values of the cells in another column. My problem is that I want the output to be progressively (cumulatively) printed. The output vector must be of the same length as the input vector. Here is a sampel table similar to the one I am dealing with:

id <- c("a", "a", "a", "b", "b", "b")
content <- c("A", "B", "A", "B", "C", "B")
(testdf <- data.frame(id, content, stringsAsFactors=FALSE))
#  id content
#1  a       A
#2  a       B
#3  a       A
#4  b       B
#5  b       C
#6  b       B

And this is want I want the result to look like:

result <- c("A", "A B", "A B A", "B", "B C", "B C B") 
result

#[1] "A"     "A B"   "A B A" "B"     "B C"   "B C B"

What I do NOT need something like this:

ddply(testdf, .(id), summarize, content_concatenated = paste(content, collapse = " "))

#  id content_concatenated
#1  a                A B A
#2  b                B C B

Upvotes: 17

Views: 4108

Answers (6)

GoGonzo
GoGonzo

Reputation: 2867

For cumulative functions I recommend runner package with runner function which can apply any algorithm on cumulative window. It can't compete with @alexis_laz solution in terms of speed, but if one needs window of certain size, lag or windows dependent on date - I would suggest to use runner.


id <- c("a", "a", "a", "b", "b", "b")
content <- c("A", "B", "A", "B", "C", "B")
testdf <- data.frame(id, content, stringsAsFactors=FALSE)

library(runner)
library(dplyr)
testdf %>%
  group_by(id) %>%
  mutate(
    result = runner(x = content, 
                    f = function(x) paste(x, collapse = " "),
                    type = "character")) # specify output type - by default numeric

For more go to documentation and vignettes

Upvotes: 1

tmfmnk
tmfmnk

Reputation: 39858

One option using dplyr and purrr could be:

testdf %>%
 group_by(id) %>%
 transmute(content_concatenated = accumulate(content, ~ paste(.x, .y)))

  id    content_concatenated
  <chr> <chr>               
1 a     A                   
2 a     A B                 
3 a     A B A               
4 b     B                   
5 b     B C                 
6 b     B C B

Upvotes: 5

alexis_laz
alexis_laz

Reputation: 13122

You could define a "cumulative paste" function using Reduce: 

cumpaste = function(x, .sep = " ") 
          Reduce(function(x1, x2) paste(x1, x2, sep = .sep), x, accumulate = TRUE)

cumpaste(letters[1:3], "; ")
#[1] "a"       "a; b"    "a; b; c"

Reduce's loop avoids re-concatenating elements from the start as it elongates the previous concatenation by the next element.

Applying it by group:

ave(as.character(testdf$content), testdf$id, FUN = cumpaste)
#[1] "A"     "A B"   "A B A" "B"     "B C"   "B C B"

Another idea, could to concatenate the whole vector at start and, then, progressively substring:

cumpaste2 = function(x, .sep = " ")
{
    concat = paste(x, collapse = .sep)
    substring(concat, 1L, cumsum(c(nchar(x[[1L]]), nchar(x[-1L]) + nchar(.sep))))
}
cumpaste2(letters[1:3], " ;@-")
#[1] "a"           "a ;@-b"      "a ;@-b ;@-c"

This seems to be somewhat faster, too:

set.seed(077)
X = replicate(1e3, paste(sample(letters, sample(0:5, 1), TRUE), collapse = ""))
identical(cumpaste(X, " --- "), cumpaste2(X, " --- "))
#[1] TRUE
microbenchmark::microbenchmark(cumpaste(X, " --- "), cumpaste2(X, " --- "), times = 30)
#Unit: milliseconds
#                  expr      min       lq     mean   median       uq      max neval cld
#  cumpaste(X, " --- ") 21.19967 21.82295 26.47899 24.83196 30.34068 39.86275    30   b
# cumpaste2(X, " --- ") 14.41291 14.92378 16.87865 16.03339 18.56703 23.22958    30  a

...which makes it the cumpaste_faster.

Upvotes: 38

akrun
akrun

Reputation: 887118

You may also try dplyr

 library(dplyr)
 res <- testdf%>%
        mutate(n=row_number()) %>%
        group_by(id) %>%
        mutate(n1=n[1L]) %>%
        rowwise() %>% 
        do(data.frame(cont_concat= paste(content[.$n1:.$n],collapse=" "),stringsAsFactors=F))

 res$cont_concat
 #[1] "A"     "A B"   "A B A" "B"     "B C"   "B C B"

Upvotes: 2

David Arenburg
David Arenburg

Reputation: 92292

data.table solution

library(data.table)
setDT(testdf)[, content2 := sapply(seq_len(.N), function(x) paste(content[seq_len(x)], collapse = " ")), by = id]
testdf

##    id content content2
## 1:  a       A        A
## 2:  a       B      A B
## 3:  a       A    A B A
## 4:  b       B        B
## 5:  b       C      B C
## 6:  b       B    B C B

Upvotes: 5

James
James

Reputation: 66834

Here's a ddply method using sapply and subsetting to paste together incrementally:

library(plyr)
ddply(testdf, .(id), mutate, content_concatenated = sapply(seq_along(content), function(x) paste(content[seq(x)], collapse = " ")))
  id content content_concatenated
1  a       A                    A
2  a       B                  A B
3  a       A                A B A
4  b       B                    B
5  b       C                  B C
6  b       B                B C B

Upvotes: 2

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