Comma-separated value files

CSVs are a common format for capturing and transferring data. Fields are usually separated by commas; sometimes by other characters, such as Tab.

Comma-separated values

Load

example.csv

Download example.csv from the link above to (e.g.) path/to/example.csv on your local filesystem. Confirm with read0, which returns the contents of a text file as a list of strings.

q)read0 `:path/to/example.csv
"id,price,qty"
"kikb,36.05,90"
"hlfe,96.57,84"
"mcej,91.34,63"
"iemn,57.12,93"
"femn,63.64,54"
"engn,94.56,38"
"edhp,63.31,97"
"ggna,72.39,88"
"mjlg,12.04,58"
"fpjb,34.3,68"
"gfpl,25.34,45"
"jogj,78.67,2"
"gpna,23.08,39"
"njoh,91.46,64"
"aoap,48.38,49"
"bhan,63.2,82"
"enmc,70,40"
"niom,58.92,88"
"nblh,42.9,77"
"jdok,9.42,30"
"plbp,42.38,17"
..

The Load CSV operator requires only a list of column types and a delimiter to return the CSV as a table.

q)show t:("SFI";enlist",") 0: `:path/to/example.csv
id   price qty
--------------
kikb 36.05 90
hlfe 96.57 84
mcej 91.34 63
iemn 57.12 93
femn 63.64 54
engn 94.56 38
edhp 63.31 97
ggna 72.39 88
mjlg 12.04 58
fpjb 34.3  68
gfpl 25.34 45
jogj 78.67 2
gpna 23.08 39
njoh 91.46 64
aoap 48.38 49
bhan 63.2  82
enmc 70    40
niom 58.92 88
nblh 42.9  77
jdok 9.42  30
..

The id column has been rendered as symbols, price as floats, and qty as ints.

Datatypes

Enlisting the delimiter (enlist",") had Load CSV interpret the first file line as column names.

Save

The simplest way to save table t as a CSV:

q)save `:path/to/t.csv
`:path/to/t.csv

Load CSV is one form of the File Text operator. Two other forms allow us finer control than save.

q)`:path/to/t.tsv 0: "\t" 0: t
`:path/to/t.tsv

Above, "\t" 0: t uses the Prepare Text form of the operator to return the table as a list of delimited strings. Here the delimiter is the Tab character "\t". The list of strings becomes the right argument to the Save Text form, which writes the strings as the lines of path/to/t.tsv.

Load Fixed for importing tables from fixed-format text files
Key-Value Pairs for interpreting key-value pairs as a dictionary
.j namespace for serializing as, and deserializing from, JSON