# Module Csv

    module Csv: sig .. end

Read and write the CSV (comma separated values) format.

This library should be compatible with RFC4180 if one sets `strip=false` in the creation functions.
Author(s): Richard Jones <rjones@redhat.com>, Christophe Troestler <Christophe.Troestler@umons.ac.be>

    type t = string list list

Representation of CSV data in memory. This is a list of rows (also called records), each row being a list of columns.

## Input/output objects

    class type in_obj_channel = object .. end

The most basic input object for best interoperability.

    class type out_obj_channel = object .. end

The most basic output object for best interoperability.

## Input

    exception Failure of int * int * string

`Failure(nrecord, nfield, msg)` is raised to indicate a parsing error for the field number `nfield` on the record number `nrecord`, the description `msg` says what is wrong. The first record and the first field of a record are numbered `1` (to correspond to the usual spreadsheet numbering but differing from `List.nth` of the OCaml representation).

    type in_channel

Stateful handle to input CSV files.

    val of_in_obj : ?separator:char ->
           ?strip:bool ->
           ?has_header:bool ->
           ?header:string list ->
           ?backslash_escape:bool ->
           ?excel_tricks:bool -> in_obj_channel -> in_channel

`of_in_obj ?separator ?excel_tricks in_chan` creates a new "channel" to access the data in CSV form available from the channel `in_chan`.
`separator` : What character the separator is. The default is `','`. You should be aware however that, in the countries where comma is used as a decimal separator, Excel will use `';'` as the separator.
`strip` : Whether to remove the white space around unquoted fields. The default is `true` for backward compatibility reasons.
`has_header` : tells that the first row of the CSV channel is to be interpreted as a header (this row will not be returned by `Csv.next`). This is useful to use the functions in the `Csv.Rows` module below. Default: `false`.
`header` : Supply the header to use for this CSV channel. If both `header` and `has_header` are given, the names of `header` take precedence; if a name in `header` is `""`, the one in the CSV header is used. If a name appears twice, only its first occurrence is used.
`backslash_escape` : Whether to allow \", \n,... in quoted fields. This is used by MySQL for example but is not standard CSV so it is set to `false` by default.
`excel_tricks` : enables Excel tricks, namely the fact that '"' followed by '0' in a quoted string means ASCII NULL and the fact that a field of the form ="..." only returns the string inside the quotes. Default: `true`.

    val of_channel : ?separator:char ->
           ?strip:bool ->
           ?has_header:bool ->
           ?header:string list ->
           ?backslash_escape:bool ->
           ?excel_tricks:bool -> Pervasives.in_channel -> in_channel

Same as `Csv.of_in_obj` except that the data is read from a standard channel.

    val of_string : ?separator:char ->
           ?strip:bool ->
           ?has_header:bool ->
           ?header:string list ->
           ?backslash_escape:bool -> ?excel_tricks:bool -> string -> in_channel

Same as `Csv.of_in_obj` except that the data is read from a string.

    val load : ?separator:char ->
           ?strip:bool ->
           ?backslash_escape:bool -> ?excel_tricks:bool -> string -> t

`load fname` loads the CSV file `fname`. If `filename` is `"-"` then load from `stdin`.
`separator` : What character the separator is. The default is `','`. You should be aware however that, in the countries where comma is used as a decimal separator, Excel will use `';'` as the separator.
`backslash_escape` : Whether to allow \", \n,... in quoted fields. This is used by MySQL for example but is not standard CSV so it is set to `false` by default.
`excel_tricks` : enables Excel tricks, namely the fact that '"' followed by '0' in a quoted string means ASCII NULL and the fact that a field of the form ="..." only returns the string inside the quotes. Default: `true`.

    val load_in : ?separator:char ->
           ?strip:bool ->
           ?backslash_escape:bool ->
           ?excel_tricks:bool -> Pervasives.in_channel -> t

`load_in ch` loads a CSV file from the input channel `ch`. See `Csv.load` for the meaning of `separator` and `excel_tricks`.

    val to_in_obj : in_channel -> in_obj_channel

For efficiency reasons, the `in_channel` buffers the data from the original channel. If you want to examine the data by other means than the methods below (say after a failure), you need to use this function in order not to "loose" data in the buffer.

    val close_in : in_channel -> unit

`close_in ic` closes the channel `ic`. The underlying channel is closed as well.

    val next : in_channel -> string list

`next ic` returns the next record in the CSV file.
Raises

- `End_of_file` if no more record can be read.
- `Csv.Failure` if the CSV format is not respected. The partial record read is available with `#current_record`.

    val fold_left : f:('a -> string list -> 'a) -> init:'a -> in_channel -> 'a

`fold_left f a ic` computes (f ... (f (f a r0) r1) ... rN) where r1,...,rN are the records in the CSV file. If `f` raises an exception, the record available at that moment is accessible through `Csv.current_record`.

    val fold_right : f:(string list -> 'a -> 'a) -> in_channel -> 'a -> 'a

`fold_right f ic a` computes (f r1 ... (f rN-1 (f rN a)) ...) where r1,...,rN-1, rN are the records in the CSV file. All records are read before applying `f` so this method is not convenient if your file is large.

    val iter : f:(string list -> unit) -> in_channel -> unit

`iter f ic` iterates `f` on all remaining records. If `f` raises an exception, the record available at that moment is accessible through `Csv.current_record`.

    val input_all : in_channel -> t

`input_all ic` return a list of the CSV records till the end of the file.

    val current_record : in_channel -> string list

The current record under examination. This is useful in order to gather the parsed data in case of `Failure`.

    val load_rows : ?separator:char ->
           ?strip:bool ->
           ?backslash_escape:bool ->
           ?excel_tricks:bool -> (string list -> unit) -> Pervasives.in_channel -> unit

Deprecated.use `Csv.iter` on a `Csv.in_channel` created with `Csv.of_channel`.

## Output

    type out_channel

    val to_out_obj : ?separator:char ->
           ?backslash_escape:bool ->
           ?excel_tricks:bool -> out_obj_channel -> out_channel

`to_out_obj ?separator ?excel_tricks out_chan` creates a new "channel" to output the data in CSV form.
`separator` : What character the separator is. The default is `','`.
`backslash_escape` : Prefer to escape the separator in a quoted string with a backslash (e.g. "\"") instead of doubling it. Also backslash-escape '\n', '\r', '\t', '\b', '\026' (as '\Z') and '\000' (as '\0') This is nice for interoperability but is nonstandard CSV to it is set to `false` by default.
`excel_tricks` : enables Excel tricks, namely the fact that '\000' is represented as '"' followed by '0' and the fact that a field with leading or trailing spaces or a leading '0' will be encoded as ="..." (to avoid Excel "helping" you). Default: `false`.

    val to_channel : ?separator:char ->
           ?backslash_escape:bool ->
           ?excel_tricks:bool -> Pervasives.out_channel -> out_channel

Same as `Csv.to_out_obj` but output to a standard channel.

    val to_buffer : ?separator:char ->
           ?backslash_escape:bool -> ?excel_tricks:bool -> Buffer.t -> out_channel

Same as `Csv.to_out_obj` but output to a buffer.

    val output_record : out_channel -> string list -> unit

`output_record oc r` write the record `r` is CSV form to the channel `oc`.

    val output_all : out_channel -> t -> unit

`output_all oc csv` outputs all records in `csv` to the channel `oc`.

    val save_out : ?separator:char ->
           ?backslash_escape:bool ->
           ?excel_tricks:bool -> Pervasives.out_channel -> t -> unit

Deprecated.Save string list list to a channel.

    val save : ?separator:char ->
           ?backslash_escape:bool -> ?excel_tricks:bool -> string -> t -> unit

`save fname csv` saves the `csv` data to the file `fname`.

    val print : ?separator:char ->
           ?backslash_escape:bool -> ?excel_tricks:bool -> t -> unit

Print the CSV data.

    val print_readable : t -> unit

Print the CSV data to `stdout` in a human-readable format. Not much is guaranteed about how the CSV is printed, except that it will be easier to follow than a "raw" output done with `Csv.print`. This is a one-way operation. There is no easy way to parse the output of this command back into CSV data.

    val save_out_readable : Pervasives.out_channel -> t -> unit

As for `Csv.print_readable`, allowing the output to be sent to a channel.

## Functions to access rows when a header is present

    module Row: sig .. end

A row with a header.

    module Rows: sig .. end

Accessing rows (when a header was provided).

## Functions acting on CSV data loaded in memory

    val lines : t -> int

Return the number of lines in a CSV data.

    val columns : t -> int

Work out the (maximum) number of columns in a CSV file. Note that each line may be a different length, so this finds the one with the most columns.

    val trim : ?top:bool -> ?left:bool -> ?right:bool -> ?bottom:bool -> t -> t

This takes a CSV file and trims empty cells.

All four of the option arguments (`~top`, `~left`, `~right`, `~bottom`) default to `true`.

The exact behaviour is:

`~right`: If true, remove any empty cells at the right hand end of any row. The number of columns in the resulting CSV structure will not necessarily be the same for each row.

`~top`: If true, remove any empty rows (no cells, or containing just empty cells) from the top of the CSV structure.

`~bottom`: If true, remove any empty rows from the bottom of the CSV structure.

`~left`: If true, remove any empty columns from the left of the CSV structure. Note that `~left` and `~right` are quite different: `~left` considers the whole CSV structure, whereas `~right` considers each row in isolation.

    val square : t -> t

Make the CSV data "square" (actually rectangular). This pads out each row with empty cells so that all rows are the same length as the longest row. After this operation, every row will have length `Csv.columns`.

    val is_square : t -> bool

Return true iff the CSV is "square" (actually rectangular). This means that each row has the same number of cells.

    val set_columns : cols:int -> t -> t

`set_columns cols csv` makes the CSV data square by forcing the width to the given number of `cols`. Any short rows are padded with blank cells. Any long rows are truncated.

    val set_rows : rows:int -> t -> t

`set_rows rows csv` makes the CSV data have exactly `rows` rows by adding empty rows or truncating rows as necessary.

Note that `set_rows` does not make the CSV square. If you want it to be square, call either `Csv.square` or `Csv.set_columns` after.

    val set_size : rows:int -> cols:int -> t -> t

`set_size rows cols csv` makes the CSV data square by forcing the size to `rows * cols`, adding blank cells or truncating as necessary. It is the same as calling `set_columns cols (set_rows rows csv)`

    val sub : r:int -> c:int -> rows:int -> cols:int -> t -> t

`sub r c rows cols csv` returns a subset of `csv`. The subset is defined as having top left corner at row `r`, column `c` (counting from `0`) and being `rows` deep and `cols` wide.

The returned CSV will be "square".

    val compare : t -> t -> int

Compare two CSV files for equality, ignoring blank cells at the end of a row, and empty rows appended to one or the other. This is "semantic" equality - roughly speaking, the two CSV files would look the same if opened in a spreadsheet program.

    val concat : t list -> t

Concatenate CSV files so that they appear side by side, arranged left to right across the page. Each CSV file (except the final one) is first squared.

(To concatenate CSV files so that they appear from top to bottom, just use `List.concat`).

    val transpose : t -> t

Permutes the lines and columns of the CSV data. Nonexistent cells become empty cells after transpose if they must be created.

    val to_array : t -> string array array

    val of_array : string array array -> t

Convenience functions to convert to and from a matrix representation. `to_array` will produce a ragged matrix (not all rows will have the same length) unless you call `Csv.square` first.

    val associate : string list -> t -> (string * string) list list

`associate header data` takes a block of data and converts each row in turn into an assoc list which maps column header to data cell.

Typically a spreadsheet will have the format:

          header1   header2   header3
          data11    data12    data13
          data21    data22    data23
          ...

This function arranges the data into a more usable form which is robust against changes in column ordering. The output of the function is:

          [ ["header1", "data11"; "header2", "data12"; "header3", "data13"];
            ["header1", "data21"; "header2", "data22"; "header3", "data23"];
            etc. ]

Each row is turned into an assoc list (see `List.assoc`).

If a row is too short, it is padded with empty cells (`""`). If a row is too long, it is truncated.

You would typically call this function as:

        let header, data = match csv with h :: d -> h, d | [] -> assert false;;
        let data = Csv.associate header data;;

The header strings are shared, so the actual space in memory consumed by the spreadsheet is not much larger.

    val map : f:(string -> string) -> t -> t

`map f csv` applies `f` to all entries of `csv` and returns the resulting CSV.