In nacnudus/unpivotr: Unpivot Complex and Irregular Data Layouts

This vignette for the unpivotr package demonstrates unpivoting multiple similar tables from a spreadsheet via the tidyxl package. It is best read with the spreadsheet open in a spreadsheet program, e.g. Excel, LibreOffice Calc or Gnumeric.

Introduction

The spreadsheet is from the famous Enron subpoena, made available by Felienne Hermans, and has has previously been publicised by Jenny Bryan and David Robinson, in particular in Robinson's article 'Tidying an untidyable dataset'.

Here's a screenshot:

knitr::include_graphics("enron-screenshot.png")

Preparation

This vignette uses several common packages.

library(unpivotr)
library(tidyxl)
library(dplyr)
library(purrr)
library(tidyr)
library(stringr)

The spreadsheet is distributed with the unpivotr package, so can be loaded as a system file.

path <- system.file("extdata/enron.xlsx", package = "unpivotr")

Main

Importing the data

Spreadsheet cells are imported with the xlsx_cells() function, which returns a data frame of all the cells in all the requested sheets. By default, every sheet is imported, but we don't have to worry about that in this case because there is only one sheet in the file. We can also straightaway discard rows above 14 and below 56, and columns beyond 20.

cells <-
  xlsx_cells(path) %>%
  dplyr::filter(!is_blank, between(row, 14L, 56L), col <= 20) %>%
  select(row, col, data_type, numeric, character, date)

Cell formatting isn't required for this vignette, but if it were, it would be imported via xlsx_formats(path).

formatting <- xlsx_formats(path)

Importing one of the multiples

The small multiples each have exactly one 'Fixed Price' header cell, so begin by filtering for those cells, and then move the selection up one row to get the title cells. The title cells are the top-left corner cell of each table.

title <-
  dplyr::filter(cells, character == "Fixed Price") %>%
  select(row, col) %>%
  mutate(row = row - 1L) %>%
  inner_join(cells, by = c("row", "col"))

Use these title cells to partition the sheet.

partitions <- partition(cells, title)

Taking one of the partitions, unpivot with behead(). The compass directions "NNW" and "N" express the direction from each data cell to its header. "NNW" means "look up and then left to find the nearest header."

partitions$cells[[1]] %>%
  behead("NNW", "title") %>%
  behead("NNW", "price") %>%
  behead("N", "bid_offer") %>%
  print(n = Inf)

The same procedure can be mapped to every small multiple.

unpivoted <-
  purrr::map_dfr(partitions$cells,
                 ~ .x %>%
                   behead("NNW", "title") %>%
                   behead("NNW", "price") %>%
                   behead("N", "bid_offer")) %>%
  select(-data_type, -character, -date)
unpivoted

So far, only the column headers have been joined, but there are also row headers on the left-hand side of the spreadsheet. The following code incorporates these into the final dataset.

row_headers <-
  cells %>%
  dplyr::filter(between(row, 17, 56), between(col, 2, 4)) %>%
  # Concatenate rows like "Dec-01", "to", "Mar-02"
  mutate(character = ifelse(!is.na(character),
                            character,
                            format(date, origin="1899-12-30", "%b-%y"))) %>%
  select(row, col, character) %>%
  nest(-row) %>%
  mutate(row_header = map(data,
                          ~ str_trim(paste(.x$character, collapse = " ")))) %>%
  unnest(row_header) %>%
  mutate(col = 2L) %>%
  select(row, row_header)
unpivoted <- left_join(unpivoted, row_headers, by = "row")
unpivoted

34-line code listing

library(unpivotr)
library(tidyxl)
library(dplyr)
library(purrr)
library(tidyr)
library(stringr)

cells <-
  xlsx_cells(system.file("extdata/enron.xlsx", package = "unpivotr")) %>%
  dplyr::filter(!is_blank, between(row, 14L, 56L), col <= 20) %>%
  select(row, col, data_type, numeric, character, date)

row_headers <-
  dplyr::filter(cells, between(row, 17, 56), between(col, 2, 4)) %>%
  mutate(character = ifelse(!is.na(character),
                            character,
                            format(date, origin="1899-12-30", "%b-%y"))) %>%
  select(row, col, character) %>%
  nest(-row) %>%
  mutate(row_header = map(data,
                          ~ str_trim(paste(.x$character, collapse = " ")))) %>%
  unnest(row_header) %>%
  mutate(col = 2L) %>%
  select(row, row_header)

titles <-
  dplyr::filter(cells, character == "Fixed Price") %>%
  select(row, col) %>%
  mutate(row = row - 1L) %>%
  inner_join(cells, by = c("row", "col"))

partition(cells, titles)$cells %>%
  purrr::map_dfr(~ .x %>%
                 behead("NNW", "title") %>%
                 behead("NNW", "price") %>%
                 behead("N", "bid_offer")) %>%
  select(-data_type, -character, -date) %>%
  left_join(row_headers, by = "row")