CODEWITHSUNDEEP
rmultidimensional-arrayapplyhigher-order-functions
Charles
Charles

Reputation: 11499

Two-dimensional apply in R?

I have two arrays

chemArr = c("water","oil",...(lots of values omitted)...,"hydrogen")
timeArr = c("0", "8hr", "12hr", "24hr", "36hr", "48hr", "72hr")

and I would like to build a data frame

chem  0               8hr               ... 72hr
water f("water", "0") f("water", "8hr") ...
...

where f is a function I have written. Is there a good way to do this in R?

In my particular case it would be more efficient to make a function taking chem and returning a column for each time, since each of these share calculations. But since the total time required is small I could do it some other way if it's more convenient.

Upvotes: 1

Views: 1204

Answers (2)

coffeinjunky
coffeinjunky

Reputation: 11514

To illustrate the solutions discussed in the comments:

one <- letters[1:3]
two <- letters[4:6]

one
[1] "a" "b" "c"
two
[1] "d" "e" "f"

mapply(paste0, one, two)
   a    b    c 
"ad" "be" "cf" 

mapply(paste0, sort(rep(one, length(two))), two)
   a    a    a    b    b    b    c    c    c 
"ad" "ae" "af" "bd" "be" "bf" "cd" "ce" "cf" 

mapply(paste0, one, list(two)) # courtesy of @thelatemail
     a    b    c   
[1,] "ad" "bd" "cd"
[2,] "ae" "be" "ce"
[3,] "af" "bf" "cf"

outer(one, two, paste0) # courtesy of @akrun
     [,1] [,2] [,3]
[1,] "ad" "ae" "af"
[2,] "bd" "be" "bf"
[3,] "cd" "ce" "cf"

Upvotes: 3

IRTFM
IRTFM

Reputation: 263499

I'd suggest using expand.grid, which creates a "long form" of all 2-way combination, and then use mapply to create the values from the function:

chemArr = c("water","oil","hydrogen")
timeArr = c("0", "8hr", "12hr", "24hr", "36hr", "48hr", "72hr")
mygrid <- expand.grid(chemArr, timeArr)
mygrid <- expand.grid(chems = chemArr, times = timeArr)
str(mygrid)
#'data.frame':  21 obs. of  2 variables:
# $ chems: Factor w/ 3 levels "water","oil",..: 1 2 3 1 2 3 1 2 3 1 ...
# $ times: Factor w/ 7 levels "0","8hr","12hr",..: 1 1 1 2 2 2 3 3 3 4 ...
# - attr(*, "out.attrs")=List of 2
#  ..$ dim     : Named int  3 7
#  .. ..- attr(*, "names")= chr  "chems" "times"
#  ..$ dimnames:List of 2
#  .. ..$ chems: chr  "chems=water" "chems=oil" "chems=hydrogen"
#  .. ..$ times: chr  "times=0" "times=8hr" "times=12hr" "times=24hr" ... 

mygrid$f_value <- mapply(f, mygrid$chems, mygrid$times)

Upvotes: 3

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