0:
File Text
Read or write text
The File Text operator 0:
has five forms:
Prepare Text table as a list of delimited strings
Save Text write a list of strings to file
Load CSV field-delimited string, list of strings, or file, as a list or matrix
Load Fixed fixed-format list of strings, or file, as a list or matrix
Key-Value Pairs delimited string as key-value pairs
Prepare Text
Represent a table as a list of delimited strings
delimiter 0: t 0:[delimiter;t]
Where
delimiter
is a char atomt
is a table
returns a list of character strings containing text representations of the rows of t
separated by delimiter
.
q)csv 0: ([]a:1 2 3;b:`x`y`z)
"a,b"
"1,x"
"2,y"
"3,z"
q)"|" 0: (`a`b`c;1 2 3;"xyz")
"a|1|x"
"b|2|y"
"c|3|z"
Any cells containing delimiter
will be embraced with "
and any embedded "
doubled.
q)t:([]x:("foo";"bar,baz";"qu\"ux";"fred\",barney"))
q)t
x
---------------
"foo"
"bar,baz"
"qu\"ux"
"fred\",barney"
q)-1@","0:t;
x
foo
"bar,baz"
qu"ux
"fred"",barney"
Q for Mortals §11.4.3 Preparing Text
Save Text
Write a list of strings to file
filesymbol 0: strings 0:[filesymbol;strings]
Where
filesymbol
is a file symbolstrings
a list of character strings
strings
are saved as lines in the file. The result of Prepare Text can be used as strings
.
q)`:test.txt 0: enlist "text to save"
`:test.txt
q)`:status.txt 0: string system "w"
`:status.txt
If filesymbol
- does not exist, it is created, with any missing containing directories
- exists, it is overwritten
Load CSV
Interpret a field-delimited string, list of strings, or file as a list or matrix
(types;delimiter ) 0: y 0:[(types;delimiter);y]
(types;delimiter;flag) 0: y 0:[(types;delimiter;flag);y]
Where
y
is a file descriptor, string, or a list of stringstypes
is a string of column type codes in upper casedelimiter
is a char atom or 1-item listflag
(optional, default0
, since V3.4) is a long atom indicating whether line-returns may be embedded in strings:0
or1
returns a vector, matrix, or table interpreted from the content of y
.
With column names
If delimiter
is enlisted, the first row of the content of y
is read as column names and the result is a table; otherwise the result is a list of values for each column.
/load 2 columns from space-delimited file with header
q)t:("SS";enlist" ")0:`:/tmp/txt
Use optional argument flag
to allow line returns embedded within strings.
q)("I*";",";1)0:("0,\"ab\nc\"";"1,\"def\"")
0 1
"ab\nc" "def"
Where y
is a string and delimiter
an atom, returns a single list of the data split and parsed accordingly.
q)("DT";",")0:"20130315,185540686"
2013.03.15
18:55:40.686
Without column names
If the CSV file contains data but no column names:
0,hea,481
10,dfi,579
20,oil,77
We can read the columns:
q)("ISI";",") 0:`data.csv
0 10 20
hea dfi oil
481 579 77
Create a column dictionary and flip it:
table: flip `a`b`c!("ISI";",") 0:`data.csv
Column names must not be the null symbol `
Load Fixed
Interpret a fixed-format list of strings or file as a list or matrix
(types; widths) 0: y 0:[(types;widths);y]
Where
y
is a file descriptor or a list of stringstypes
is a list of column types in upper casewidths
is an int vector of field widths
returns a vector or matrix interpreted from the content of y
.
q)sum("DT";8 9)0:enlist"20130315185540686"
,2013.03.15D18:55:40.686000000
q)("DT";8 9)0:("20130315185540686";"20130315185540686")
2013.03.15 2013.03.15
18:55:40.686 18:55:40.686
q)dates:("Tue, 04 Jun 2013 07:00:13 +0900";"Tue, 04 Jun 2013 07:00:13 -0500")
q)sum(" Z T";5 20 1 5)0:dates
2013.06.04T16:00:13.000 2013.06.04T02:00:13.000
Load Fixed expects either a \n
after every record, or none at all.
/reads a text file containing fixed-length records
q)t:("IFC D";4 8 10 6 4) 0: `:/q/Fixed.txt
Tips for Load CSV and Load Fixed
- To load a field as a nested character column or list rather than symbol use
"*"
as the identifier - To omit a field from the load use
" "
.
Key-Value Pairs
Interpret a delimited string as key-value pairs
x 0: string 0:[x;string]
Where x
is a 3- or 4-char string:
key-type
field-separator
[asterisk]
record-separator
and key-type
is S
for symbol, I
for integer, or J
for long, returns a 2-row matrix of the keys and values.
q)"S=;"0:"one=1;two=2;three=3"
one two three
,"1" ,"2" ,"3"
q)"S:/"0:"one:1/two:2/three:3"
one two three
,"1" ,"2" ,"3"
q)"I=;"0:"1=first;2=second;3=third"
1 2 3
"first" "second" "third"
q)s:"8=FIX.4.2\0019=339\00135=D\00134=100322\00149=JM_TEST1\00152=20130425-06:46:46.387"
q)(!/)"I=\001"0:s
8 | "FIX.4.2"
9 | "339"
35| ,"D"
34| "100322"
49| "JM_TEST1"
52| "20130425-06:46:46.387"
The inclusion of an asterisk as the third character allows the delimiter character to appear harmlessly in quoted strings. (Since V3.5.)
q)0N!"I=*,"0:"5=\"hello,world\",6=1";
(5 6i;("hello,world";,"1"))
q)0N!"J=*,"0:"5=\"hello,world\",6=1";
(5 6;("hello,world";,"1"))
q)0N!"S=*,"0:"a=\"hello,world\",b=1";
(`a`b;("hello,world";,"1"))
Q for Mortals §11.5.3 Key-Value Records
Column types and formats
B boolean /[01tfyn]/i
G guid /[0-9a-f]{8}(-[0-9a-f]{4}){3}-[0-9a-f]{12}/i
X byte
H short [0-9][0-9]
I int
J long
E real
F float
C char
S symbol
P timestamp date?timespan
M month [yy]yy[?]mm
D date [yy]yy[?]mm[?]dd or [m]m/[d]d/[yy]yy
Z datetime date?time
N timespan hh[:]mm[:]ss[[.]ddddddddd]
U minute hh[:]mm
V second hh[:]mm[:]ss
T time hh[:]mm[:]ss[[.]ddd]
(blank) skip
* literal chars
.j
namespace for JSON
Datatypes,
File system
How do I import a CSV file into a table?
Q for Mortals
§11.4.1 Reading and Writing Text Files