我想按一列汇总，然后取一列的总和和另一列的平均值

Question

下面是我目前用来总结我的数据的代码，它正在工作。我的问题是我想实际取“CE100”列的平均值与总和。我怎样才能操纵下面的代码来做到这一点？

library(data.table, warn.conflicts = FALSE)
library(magrittr)   ### MODIFIED
# library(lubridate, warn.conflicts = FALSE)   ### MODIFIED

################
## PARAMETERS ##
################

# Set path of major source folder for raw transaction data
in_directory <- "C:/Users/NAME/Documents/Raw Data/"

# List names of sub-folders (currently grouped by first two characters of CUST_ID)
in_subfolders <- list("AA-CA", "CB-HZ", "IA-IL", "IM-KZ", "LA-MI", "MJ-MS",
                      "MT-NV", "NW-OH", "OI-PZ", "QA-TN", "TO-UZ",
                      "VA-WA", "WB-ZZ")

# Set location for output
out_directory <- "C:/Users/NAME/Documents/YTD Master/"
out_filename <- "OUTPUT.csv"


# Set beginning and end of date range to be collected - year-month-day format
date_range <- c("2018-01-01", "2018-06-30")   ### MODIFIED

# Enable or disable filtering of raw files to only grab items bought within certain months to save space.
# If false, all files will be scanned for unique items, which will take longer and be a larger file.
# date_filter <- TRUE   ### MODIFIED


##########
## CODE ##
##########

starttime <- Sys.time()

# create vector of filenames to be processed
in_filenames <- list.files(
  file.path(in_directory, in_subfolders), 
  pattern = "\\.txt$", 
  full.names = TRUE, 
  recursive = TRUE)

# filter filenames, only 
selected_in_filenames <- 
  seq(as.Date(date_range[1]), 
      as.Date(date_range[2]), by = "1 month") %>% 
  format("%Y-%m") %>% 
  lapply(function(x) stringr::str_subset(in_filenames, x)) %>% 
  unlist()


# read and aggregate each file separetely
mastertable <- rbindlist(
  lapply(selected_in_filenames, function(fn) {
    message("Processing file: ", fn)
    temptable <- fread(fn,
                       colClasses = c(CUSTOMER_TIER = "character"),
                       na.strings = "")

    { # Add columns
      print(paste0("Adding columns - ", subfolder, " (", j," of ", length(in_subfolders), ")"))
      print(Sys.time()-starttime)
      temptable[, ':='(CustPart = paste0(CUST_ID, INV_ITEM_ID))]}

    # aggregate file but filtered for date_range
    temptable[INVOICE_DT %between% date_range, 
              lapply(.SD, sum), by = .(CustPart, QTR = quarter(INVOICE_DT), YEAR = year(INVOICE_DT)), 
              .SDcols = c("Ext Sale", "CE100")]
  })
)[
  # second aggregation overall
  , lapply(.SD, sum), by = .(CustPart, QTR, YEAR), .SDcols = c("Ext Sale", "CE100")]

# Save Final table
print("Saving master table")
fwrite(mastertable, file.path(out_directory, out_filename))
# rm(mastertable)   ### MODIFIED

print(Sys.time()-starttime)

mastertable

我已经包含了我的所有代码，以显示我如何读取我的数据。如果需要任何其他细节，比如一些示例数据，请告诉我。

Answer 1

OP 方法的关键点是交错聚合（参见相关问题row not consolidating duplicates in R when using multiple months in Date Filter）。

OP 希望跨多个文件聚合数据，这些文件显然太大而无法完全加载并合并到一个大型 data.table 中。

相反，每个文件都是单独读入和聚合的。小计被合并到一个 data.table 中，在第二个聚合步骤中计算总和。

现在，OP 希望在聚合步骤中包含总和以及平均值。交错聚合适用于总和和计数，但不适用于平均值，例如，mean(1:5) 这是 3 与小计 mean(1:2) 和 mean(3:5) 的平均值不同：mean(c(mean(1:2), mean(3:5))) 是 2.75。

因此，以下方法仅计算第一个和第二个聚合步骤的总和和计数，并分别计算所选列的平均值。 数据取自OP's other question。此外，by = 参数为演示而简化，data.range 已适应示例数据。

library(data.table, warn.conflicts = FALSE)
library(magrittr)   ### MODIFIED
# library(lubridate, warn.conflicts = FALSE)   ### MODIFIED

################
## PARAMETERS ##
################

# Set path of major source folder for raw transaction data
in_directory <- "Raw Data"

# List names of sub-folders (currently grouped by first two characters of CUST_ID)
in_subfolders <- list("AA-CA", "CB-HZ", "IA-IL", "IM-KZ", "LA-MI", "MJ-MS",
                      "MT-NV", "NW-OH", "OI-PZ", "QA-TN", "TO-UZ",
                      "VA-WA", "WB-ZZ")

# Set location for output
out_directory <- "YTD Master"
out_filename <- "OUTPUT.csv"


# Set beginning and end of date range to be collected - year-month-day format
date_range <- c("2017-01-01", "2017-06-30")   ### MODIFIED

# Enable or disable filtering of raw files to only grab items bought within certain months to save space.
# If false, all files will be scanned for unique items, which will take longer and be a larger file.
# date_filter <- TRUE   ### MODIFIED


##########
## CODE ##
##########

starttime <- Sys.time()

# create vector of filenames to be processed
in_filenames <- list.files(
  file.path(in_directory, in_subfolders), 
  pattern = "\\.txt$", 
  full.names = TRUE, 
  recursive = TRUE)

# filter filenames
selected_in_filenames <- 
  seq(as.Date(date_range[1]), 
      as.Date(date_range[2]), by = "1 month") %>% 
  format("%Y-%m") %>% 
  lapply(function(x) stringr::str_subset(in_filenames, x)) %>% 
  unlist()


# read and aggregate each file separetely
mastertable <- rbindlist(
  lapply(selected_in_filenames, function(fn) {
    message("Processing file: ", fn)
    temptable <- fread(fn,
                       colClasses = c(CUSTOMER_TIER = "character"),
                       na.strings = "")

    # aggregate file but filtered for date_range
    temptable[INVOICE_DT %between% date_range, 
              c(.(N = .N), lapply(.SD, sum)), 
              by = .(CUST_ID, 
                     QTR = quarter(INVOICE_DT), YEAR = year(INVOICE_DT)), 
              .SDcols = c("Ext Sale", "CE100")] 
  })
)[
  # second aggregation overall
  , lapply(.SD, sum), 
  by = .(CUST_ID, QTR, YEAR), 
  .SDcols = c("N", "Ext Sale", "CE100")]
# update mastertable with averages of selected columns
cols_avg <- c("CE100")
mastertable[, (cols_avg) := lapply(.SD, function(x) x/N), 
    .SDcols = cols_avg]

# Save Final table
print("Saving master table")
fwrite(mastertable, file.path(out_directory, out_filename))
# rm(mastertable)   ### MODIFIED

print(Sys.time()-starttime)

mastertable

     CUST_ID QTR YEAR N Ext Sale      CE100
1: AK0010001   1 2017 4  427.803 29.4119358
2: CO0020001   1 2017 2 1540.300         NA
3: CO0010001   1 2017 2 -179.765  0.0084625

缺失值包含在聚合中。需要在业务方面决定如何处理缺失值。如果要从聚合中排除缺失值，则平均值的交错计算可能会变得更加复杂。