CSV to APL

CSV stands for comma separated values. Those files are still used to transport tabular data between applications that are not directly connected. The files can be edited with any spreadsheet application like Microsoft Excel.

There are some things one need to know about CSV file in order to deal with them:

• Fields are separated by commas
• Records are separated with system end of line characters, CRLF (ASCII 13 Dec or 0D Hex and ASCII 10 Dec or 0A Hex respectively) for Windows, LF for Unix, and CR for Mac
• If a field contains either a comma or one of the end line chars, either the char(s) or the whole contents needs to be escaped. Excel escapes these values by embedding the field inside a set of double quotes. For example, a single cell with the text apples, carrots, and oranges becomes "apples, carrots, and oranges"

• Strictly speaking, the delimiter is not defined in the specs. Some banks offer downloads where a semicolon is used instead of a comma. You might wonder why the name of this format is Comma Seperated Values, so, but anyway.

For details and background information see http://www.csvreader.com/csv_format.php

Note that the format comes with a nasty built-in-problem: there is no way to recognize a cell as being numeric. Converting cells which only contain a proper number does not help because if you enter a digit with a leading quote, Excel handles this as text but again this cannot be recognized as text in the csv file. The only solution is therefore to make an informed guess.

Reading a CSV file

Given an Excel spreadsheet that looks like this:

Saving this into a csv file, the file can be read into APL. The variable would look like this:

To convert this into an APL matrix is a two-step-process:

• partition the simple string from file
• extract the data and build up the APL matrix

First Step: Partition The String Being Read From File

With the following two functions this variable can be transformed into an APL array where every item represents a record. Data masked by " remain unchanged. The functions can deal with files from Unix, Mac and Windows.

r←{ignoreBetween}PartitionRecordsWithDyalog string;masked;cr;lf;bool
⍝ Takes a string and partitions records.
⍝ Can deal with Mac/Unix/Windows files.
⍝ For that, CR+LF as well as single LFs are converted into CR.
⍝ CR is then used to partition "string".
⍝ Note that everything between "ignoreBetween" is ignored.
⍝ This can be used to masked stuff between "" (CSV files), for example.
 ⎕IO←1 ⋄ ⎕ML←3
 (cr lf)←⎕TC[2 3]                         ⍝ <CarriageReturn> and <LineFeed>
 :If 0=⎕NC'ignoreBetween'
     ignoreBetween←''                     ⍝ establish default
 :EndIf
 :If ~masked←0∊⍴ignoreBetween
     masked←~{⍵∨≠\⍵}'"'=string            ⍝ what is not escaped (between "")
 :EndIf
 :If 0∊bool←~(cr,lf)⍷masked/string        ⍝ are there any unmasked cr/lf in "string"?
     bool←(~masked)∨masked\bool           ⍝ "insert" the masked
     string[1+{⍵/⍳⍴⍵}~bool]←cr            ⍝ convert lf into cr
     string←bool/string                   ⍝ remove original cr
     masked←bool/masked
 :ElseIf 1∊bool←lf=masked/string          ⍝ Are there any unmasked lf in "string"?
     ((masked\bool)/string)←cr            ⍝ change them to cr
 :EndIf
 r←¯1↓(+\1,1↓masked\cr=masked/string)⊂string
 r←(0,1↓1⍴⍨⍴r)↓¨r

Second Step: Extract The Real Data

r←{sep}Csv2MatrixWithDyalog csv;bool;⎕IO;buffer;isNum
⍝ Convert vector-of-text-vectors "csv" that is assumed to
⍝ come from  a *.csv file and which got already partinioned
⍝ into an APL matrix. Takes care of escaped stuff.
⍝ "sep" defaults to a comma but that can be changed by specifying a left argument.
 ⎕IO←1 ⋄ ⎕ML←3
 sep←{2=⎕NC ⍵:⍎⍵ ⋄ ','}'sep'
 r←(⌽∨\0≠⌽↑∘⍴¨csv)/csv          ⍝ remove empty stuff from the end if any
 bool←{~{⍵∨≠\⍵}'"'=⍵}¨r         ⍝ prepare booleans useful to mask escaped stuff
 r←⊃r{⍺⊂⍨⍵≠sep}¨bool{⍺\⍺/⍵}¨r   ⍝ partition fields by unmasked commas
 r←{'"'≠1⍴⍵:⍵ ⋄ ¯1↓1↓⍵}¨r       ⍝ remove leading and trailing "
 buffer←{0=+/bool←'-'=w←⍵:⍵ ⋄ (bool/w)←'¯' ⋄ w}¨r  ⍝ "buffer" is a copy of r with "¯" for "-"
 buffer←{0=+/bool←','=w←⍵:⍵ ⋄ (bool/w)←'.' ⋄ w}¨buffer  ⍝ "," gets "."
 r←buffer{↑1⊃v←⎕VFI ⍺:↑2⊃v ⋄ ⍵}¨r ⍝ make fields whith appropriate content numeric scalars

The Final Step

Put it all together:

 r←DealWithCsv filename;data
⍝ Read "filename" which is assumed to be a *.csv file 
⍝ and converts it into a matrix
 data←FileRead filename
 data←'"'PartitionRecordsWithDyalog data
 r←Csv2MatrixWithDyalog data

The resulting variable in APL would look like this:

Note that the 1 in the second row/second column got converted into the number because the contents of the cell remained of digits only. However, in the original Excel spreadsheet that cell is text; this is indicated by the small green triangle. This information is not contained in the CSV file.

Writing a CSV file

Given an APL array like:

   ⎕←2 3⍴'APL' 'is' 'fine, very fine' 1 2.2 ¯3
 APL   is  fine, very fine 
   1  2.2    ¯3 

The following functions take such an array as right argument and convert it into a string that can be written to a file with the extension ".csv". The left argument defaults to "windows" and can be "unix" or "mac" as well. Note that the left argument is case sensitive. The left argument is used to determine the appropriate record separator.

 r←{os}Array2CsvWithDyalog array;cr;lf;sep;bool;IsChar
 ⎕IO←1 ⋄ ⎕ML←3
 :If 0=⎕NC'os'
     os←'windows'
 :EndIf
 'Invalid left argument; must be one of: windows, unix, mac'⎕SIGNAL 11/⍨~(⊂os)∊'windows' 'unix' 'mac'
 'Right argument must have a depth of 2'⎕SIGNAL 11/⍨2≠≡array
 'Right argument must be either a matrix or a vector'⎕SIGNAL 11/⍨~(⍴⍴array)∊1 2
 (cr lf)←⎕TC[2 3]                                ⍝ <CarriageReturn> and <LineFeed>
 sep←('windows' 'unix' 'mac'⍳⊂os)⊃(cr,lf)lf cr   ⍝ select proper record separator
 IsChar←{0 2∊⍨10|⎕DR ⍵}                          ⍝ Version 12 compatible
 bool←,~IsChar¨array                             ⍝ locate number
 (bool/,array)←⍕¨bool/,array                     ⍝ make numbers text
 bool←,(lf∊¨array)∨','∊¨array                    ⍝ where are special chars used?
 (bool/,array)←{'"',⍵,'"'}¨bool/,array           ⍝ escape field with special chars
 array←{⊃{⍺,',',⍵}/⍵}¨↓array                     ⍝ separate fields by comma
 r←⊃,/array,¨⊂sep                                ⍝ make it simpel
 ((r='¯')/r)←'-'                                 ⍝ Handle ¯

⍝ Example:
   #.Array2Csv 2 3⍴'APL' 'is' 'fine, very fine' 1 2.2 ¯3
APL,is,"fine, very fine"            

1,2.2,-3                            

Author: KaiJaeger