Optimize calls to mutate and summarise?

Question

I have this R script:

rm(list = ls())

library(tidyr)
suppressWarnings(library(dplyr))
outFile = "zFinal.lua"

cat("\014\n")

cat(file = outFile, sep = "")

filea <- read.csv("csva.csv", strip.white = TRUE)
fileb <- read.csv("csvb.csv", strip.white = TRUE, sep = ";", header=FALSE)

df <-    
    merge(filea, fileb, by.x = c(3), by.y = c(1)) %>%
    subset(select = c(1, 3, 6, 2)) %>%
    arrange(ColA, ColB, V2) %>%
    group_by(ColA) %>%
    mutate(V2 = paste0('"', V2, "#", ColB, '"')) %>%
    summarise(ID = paste(V2, collapse = ", ", sep=";")) %>%
    mutate(ID = paste0('["', ColA, '"] = {', ID, '},')) %>%
    mutate(ID = paste0('\t\t', ID))

df <- df[c("ID")]

cat("\n\tmyTable = {\n", file = outFile, append = TRUE, sep = "\n")
write.table(df, append = TRUE, file = outFile, sep = ",", quote = FALSE, row.names = FALSE, col.names = FALSE)
cat("\n\t}", file = outFile, append = TRUE, sep = "\n")

# Done
cat("\nDONE.", sep = "\n")

As you can see, this script opens csva.csv and csvb.csv.

This is csva.csv:

ID,ColA,ColB,ColC,ColD
2,3,100,1,1
3,7,300,1,1
5,7,200,1,1
11,22,900,1,1
14,27,500,1,1
16,30,400,1,1
20,36,900,1,1
23,39,800,1,1
24,42,700,1,1
29,49,800,1,1
45,3,200,1,1

And this is csvb.csv:

100;file1
200;file2
300;file3
400;file4

This is the output file that my script and the csv files produce:

myTable = {

    ["3"] = {"file1#100", "file2#200"},
    ["7"] = {"file2#200", "file3#300"},
    ["30"] = {"file4#400"},

}

This output file is exactly what I want. It's perfect.

This is what the script does. I'm not sure I can explain this very well so if I don't do a good job at that, please skip this section.

For each line in csva.csv, if ColC (csva) contains a number that is contained in Column 1 (csvb), then the output file should contain a line like this:

["3"] = {"file1#100", "file2#200"},

So, in the above example, the first line in ColA (csva) contains number 3 and colB for that line is 100. In csvb, column 1 contains 100 and column 2 contains file1#100.

Because csva contains another number 3 in ColA (the last line), this is also processed and output to the same line.

Ok so my script runs very well indeed and produces perfect output. The problem is it takes too long to run. csva and csvb in my question here are only a few lines long so the output is instant.

However, the data I have to work with in the real world - csva is over 300,000 lines and csvb is over 900,000 lines. So the script takes a long, long time to run (too long to make it feasible). It does work beautifully but it takes far too long to run.

From commenting out lines gradually, it seems that the slowdown is with mutate and summarise. Without those lines, the script runs in about 30 seconds. But with mutate and summarise, it takes hours.

I'm not too advanced with R so how can I make my script run faster possibly by improving my syntax or providing faster alternatives to mutate and summarise?

Answer 1

Here's another solution that leverages data.table's performance while still staying within your dplyr knowledge. I'm not sure there's much room to improve within only 10 seconds, but theoretically this could help larger datasets where the cost to create the indexes is amortized over a longer stretch of execution.

The dtplyr package is translating the dplyr verbs (that are familiar to you) to data.table syntax under the hood. That's leveraging the keys, which should improve the performance, especially with joining and grouping.

The dtplyr::lazy_dt feature might help optimize the dplyr-to-data.table translation.

Finally, vroom replaces readr, mostly out of curiosity. But it's independent from the other changes, and it sounds like that's never been a bottleneck

col_types_a <- vroom::cols_only(
  `ID`      = vroom::col_integer(),
  `ColA`    = vroom::col_integer(),
  `ColB`    = vroom::col_integer(),
  `ColC`    = vroom::col_integer()
  # `ColD`    = vroom::col_integer() # Leave out this column b/c it's never used
)
col_types_b <- vroom::cols_only(
  `ColB`      = vroom::col_integer(),
  `file_name` = vroom::col_character()
)
ds_a <- vroom::vroom(str_a, col_types = col_types_a)
ds_b <- vroom::vroom(str_b, delim = ";", col_names = c("ColB", "file_name"), col_types = col_types_b)

# ds_a <- data.table::setDT(ds_a, key = c("ColB", "ColA"))
# ds_b <- data.table::setDT(ds_b, key = "ColB")

ds_a <- dtplyr::lazy_dt(ds_a, key_by = c("ColB", "ColA"))    # New line 1
ds_b <- dtplyr::lazy_dt(ds_b, key_by = "ColB")               # New line 2

ds_a %>% 
  dplyr::select( # Quickly drop as many columns as possible; avoid reading if possible
    ID,
    ColB,
    ColA
  ) %>%
  dplyr::inner_join(ds_b, by = "ColB") %>%                   # New line 3 (replaces left join)
  # tidyr::drop_na(file_name) %>%                            # Remove this line
  # dplyr::filter(!is.na(file_name)) %>%                     # Alternative w/ left join
  dplyr::mutate(
    entry = paste0('"', file_name, "#", ColB, '"')
  ) %>%
  dplyr::select( # Dump the uneeded columns
    -ID,
    -file_name
  ) %>% 
  dplyr::group_by(ColA) %>%
  dplyr::arrange(ColB, entry) %>%  # Sort inside the group usually helps
  dplyr::summarise(
    entry = paste(entry, collapse = ", ", sep=";")
  ) %>%
  dplyr::ungroup() %>% 
  dplyr::mutate(
    entry = paste0('\t\t["', ColA, '"] = {', entry, '},')
  ) %>% 
  dplyr::pull(entry) %>% # Isolate the desired vector
  paste(collapse = "\n") %>% 
  cat()

Answer 2

Here is a more compact version of your code in base R that should offer something of a performance boost.

(Edited to match the data provided by wibeasley.)

ds_a$file_name <- ds_b$file_name[match(ds_a$ColB, ds_b$ColB)]
ds_a <- ds_a[!is.na(ds_a$file_name), -4]
ds_a <- ds_a[order(ds_a$ColB),]
ds_a$file_name <- paste0('"', ds_a$file_name, "#", ds_a$ColB, '"')
res <- tapply(ds_a$file_name, ds_a$ColA, FUN = paste,  collapse = ", ", sep=";")
res <- paste0("\t\t[\"", names(res), "\"] = {", res, "},", collapse = "\n")
cat("\n\tmyTable = {", res, "\t}", sep = "\n\n")

Outputting:

myTable = {

    ["3"] =  {"file1#100", "file2#200"},
    ["7"] =  {"file2#200", "file3#300"},
    ["30"] =  {"file4#400"},

}

Answer 3

Here's a dplyr approach that closely follows yours. The real differences are that rows and columns are dropped from the object as soon as possible so there's less baggage to move around.

I'm making some guesses what will actually help with the large datasets. Please report back what the before & after durations are. I like how you said which calls were taking the longest; reporting the new bottles would help too.

If this isn't fast enough, the next easiest move is probably move to sqldf (which uses SQLite under the cover) or data.table. Both require learning a different syntax (unless you already know sql), but could be worth your time in the long run.

# Pretend this info is being read from a file
str_a <-
"ID,ColA,ColB,ColC,ColD
2,3,100,1,1
3,7,300,1,1
5,7,200,1,1
11,22,900,1,1
14,27,500,1,1
16,30,400,1,1
20,36,900,1,1
23,39,800,1,1
24,42,700,1,1
29,49,800,1,1
45,3,200,1,1"

str_b <-
"100;file1
200;file2
300;file3
400;file4"


# Declare the desired columns and their data types.
#   Include only the columns needed.  Use the smaller 'integer' data type where possible.
col_types_a <- readr::cols_only(
  `ID`      = readr::col_integer(),
  `ColA`    = readr::col_integer(),
  `ColB`    = readr::col_integer(),
  `ColC`    = readr::col_integer()
  # `ColD`    = readr::col_integer() # Exclude columns never used
)
col_types_b <- readr::cols_only(
  `ColB`      = readr::col_integer(),
  `file_name` = readr::col_character()
)

# Read the file into a tibble
ds_a <- readr::read_csv(str_a, col_types = col_types_a)
ds_b <- readr::read_delim(str_b, delim = ";", col_names = c("ColB", "file_name"), col_types = col_types_b)

ds_a %>% 
  dplyr::select( # Quickly drop as many columns as possible; avoid reading if possible
    ID,
    ColB,
    ColA
  ) %>% 
  dplyr::left_join(ds_b, by = "ColB") %>% # Join the two datasets
  tidyr::drop_na(file_name) %>%           # Dump the records you'll never use
  dplyr::mutate(                          # Create the hybrid column
    entry = paste0('"', file_name, "#", ColB, '"')
  ) %>%
  dplyr::select(                          # Dump the unneeded columns
    -ID,
    -file_name
  ) %>% 
  dplyr::group_by(ColA) %>%               # Create a bunch of subdatasets
  dplyr::arrange(ColB, entry) %>%         # Sorting inside the group usually is faster?
  dplyr::summarise(
    entry = paste(entry, collapse = ", ", sep = ";")
  ) %>%
  dplyr::ungroup() %>%                    # Stack all the subsets on top of each other
  dplyr::mutate(                          # Mush the two columns
    entry = paste0('\t\t["', ColA, '"] = {', entry, '},')
  ) %>% 
  dplyr::pull(entry) %>%                  # Isolate the desired vector
  paste(collapse = "\n") %>%              # Combine all the elements into one.
  cat()

result:

        ["3"] = {"file1#100", "file2#200"},
        ["7"] = {"file2#200", "file3#300"},
        ["30"] = {"file4#400"},

Answer 4

you could try to load your table as a data.table instead. usually data.tables are faster in their operations than data.frames

library(data.table)
filea <- fread("csva.csv")

just check that it is still a data.table before you come to the mutate function (just print it, you will see the obvious difference to the data.frame).