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#' Read a fixed width file into a tibble
#'
#' A fixed width file can be a very compact representation of numeric data.
#' It's also very fast to parse, because every field is in the same place in
#' every line. Unfortunately, it's painful to parse because you need to
#' describe the length of every field. Readr aims to make it as easy as possible
#' by providing a number of different ways to describe the field structure.
#'
#' @seealso [read_table()] to read fixed width files where each
#' column is separated by whitespace.
#' @inheritParams datasource
#' @inheritParams tokenizer_fwf
#' @inheritParams read_delim
#' @param col_positions Column positions, as created by [fwf_empty()],
#' [fwf_widths()] or [fwf_positions()]. To read in only selected fields,
#' use [fwf_positions()]. If the width of the last column is variable (a
#' ragged fwf file), supply the last end position as NA.
#' @export
#' @examples
#' fwf_sample <- readr_example("fwf-sample.txt")
#' cat(read_lines(fwf_sample))
#'
#' # You can specify column positions in several ways:
#' # 1. Guess based on position of empty columns
#' read_fwf(fwf_sample, fwf_empty(fwf_sample, col_names = c("first", "last", "state", "ssn")))
#' # 2. A vector of field widths
#' read_fwf(fwf_sample, fwf_widths(c(20, 10, 12), c("name", "state", "ssn")))
#' # 3. Paired vectors of start and end positions
#' read_fwf(fwf_sample, fwf_positions(c(1, 30), c(20, 42), c("name", "ssn")))
#' # 4. Named arguments with start and end positions
#' read_fwf(fwf_sample, fwf_cols(name = c(1, 20), ssn = c(30, 42)))
#' # 5. Named arguments with column widths
#' read_fwf(fwf_sample, fwf_cols(name = 20, state = 10, ssn = 12))
read_fwf <- function(file, col_positions, col_types = NULL,
locale = default_locale(), na = c("", "NA"),
comment = "", trim_ws = TRUE, skip = 0, n_max = Inf,
guess_max = min(n_max, 1000), progress = show_progress(),
skip_empty_rows = TRUE) {
ds <- datasource(file, skip = skip, skip_empty_rows = skip_empty_rows)
if (inherits(ds, "source_file") && empty_file(file)) {
return(tibble::tibble())
}
tokenizer <- tokenizer_fwf(col_positions$begin, col_positions$end, na = na, comment = comment, trim_ws = trim_ws, skip_empty_rows = skip_empty_rows)
spec <- col_spec_standardise(
file,
skip = skip,
guess_max = guess_max,
tokenizer = tokenizer,
locale = locale,
col_names = col_positions$col_names,
col_types = col_types,
drop_skipped_names = TRUE
)
if (is.null(col_types) && !inherits(ds, "source_string")) {
show_cols_spec(spec)
}
out <- read_tokens(datasource(file, skip = spec$skip, skip_empty_rows = skip_empty_rows), tokenizer, spec$cols, names(spec$cols),
locale_ = locale, n_max = if (n_max == Inf) -1 else n_max,
progress = progress)
out <- name_problems(out, names(spec$cols), source_name(file))
attr(out, "spec") <- spec
warn_problems(out)
}
#' @rdname read_fwf
#' @export
#' @param n Number of lines the tokenizer will read to determine file structure. By default
#' it is set to 100.
fwf_empty <- function(file, skip = 0, skip_empty_rows = FALSE, col_names = NULL, comment = "", n = 100L) {
ds <- datasource(file, skip = skip, skip_empty_rows = skip_empty_rows)
out <- whitespaceColumns(ds, comment = comment, n = n)
out$end[length(out$end)] <- NA
col_names <- fwf_col_names(col_names, length(out$begin))
out$col_names <- col_names
out
}
#' @rdname read_fwf
#' @export
#' @param widths Width of each field. Use NA as width of last field when
#' reading a ragged fwf file.
#' @param col_names Either NULL, or a character vector column names.
fwf_widths <- function(widths, col_names = NULL) {
pos <- cumsum(c(1L, abs(widths)))
fwf_positions(pos[-length(pos)], pos[-1] - 1L, col_names)
}
#' @rdname read_fwf
#' @export
#' @param start,end Starting and ending (inclusive) positions of each field.
#' Use NA as last end field when reading a ragged fwf file.
fwf_positions <- function(start, end = NULL, col_names = NULL) {
stopifnot(length(start) == length(end))
col_names <- fwf_col_names(col_names, length(start))
tibble(
begin = start - 1L,
end = end, # -1 to change to 0 offset, +1 to be exclusive,
col_names = as.character(col_names)
)
}
#' @rdname read_fwf
#' @export
#' @param ... If the first element is a data frame,
#' then it must have all numeric columns and either one or two rows.
#' The column names are the variable names. The column values are the
#' variable widths if a length one vector, and if length two, variable start and end
#' positions. The elements of `...` are used to construct a data frame
#' with or or two rows as above.
fwf_cols <- function(...) {
x <- lapply(list(...), as.integer)
names(x) <- fwf_col_names(names(x), length(x))
x <- tibble::as_tibble(x)
if (nrow(x) == 2) {
fwf_positions(as.integer(x[1, ]), as.integer(x[2, ]), names(x))
} else if (nrow(x) == 1) {
fwf_widths(as.integer(x[1, ]), names(x))
} else {
stop("All variables must have either one (width) two (start, end) values.",
call. = FALSE)
}
}
fwf_col_names <- function(nm, n) {
nm <- nm %||% rep("", n)
nm_empty <- (nm == "")
nm[nm_empty] <- paste0("X", seq_len(n))[nm_empty]
nm
}