Module pl.data
Reading and querying simple tabular data.
data.read 'test.txt' ==> {{10,20},{2,5},{40,50},fieldnames={'x','y'},delim=','}Provides a way of creating basic SQL-like queries.
require 'pl' local d = data.read('xyz.txt') local q = d:select('x,y,z where x > 3 and z < 2 sort by y') for x,y,z in q do print(x,y,z) end
See the Guide
Functions
Data.column_by_name (name) | return a particular column as a list of values (Method). |
Data.select (condn) | return a query iterator on this data object (Method). |
Data.copy_select (condn) | return a new data object based on this query (Method). |
Data.column_names () | return the field names of this data object (Method). |
Data.write_row (f) | write out a row (Method). |
Data.write (f) | write data out to file(Method). |
read (file, cnfg) | read a delimited file in a Lua table. |
new (d, fieldnames) | create a new dataset from a table of rows. |
query (data, condn, context, return_row) | create a query iterator from a select string. |
filter (Q, infile, outfile, dont_fail) | Filter input using a query. |
Functions
- Data.column_by_name (name)
-
return a particular column as a list of values (Method).
Parameters:
name
: either name of column, or numerical index.
- Data.select (condn)
-
return a query iterator on this data object (Method).
Parameters:
condn
: the query expression
see also:
- Data.copy_select (condn)
-
return a new data object based on this query (Method).
Parameters:
condn
: the query expression
- Data.column_names ()
-
return the field names of this data object (Method).
- Data.write_row (f)
-
write out a row (Method).
Parameters:
f
: file-like object
- Data.write (f)
-
write data out to file(Method).
Parameters:
f
: file-like object
- read (file, cnfg)
-
read a delimited file in a Lua table.
By default, attempts to treat first line as separated list of fieldnames.
Parameters:
file
: a filename or a file-like object (default stdin)cnfg
: options table: can override delim (a string pattern), fieldnames (a list), specify no_convert (default is to convert), numfields (indices of columns known to be numbers) and thousands_dot (thousands separator in Excel CSV is '.')
- new (d, fieldnames)
-
create a new dataset from a table of rows.
Can specify the fieldnames, else the table must have a field called 'fieldnames', which is either a string of delimiter-separated names, or a table of names.
If the table does not have a field called 'delim', then an attempt will be made to guess it from the fieldnames string, defaults otherwise to tab.Parameters:
d
: the table.fieldnames
: optional fieldnames
Returns:
-
the table.
- query (data, condn, context, return_row)
-
create a query iterator from a select string.
Select string has this format:
FIELDLIST [ where LUA-CONDN [ sort by FIELD] ]
FIELDLISt is a comma-separated list of valid fields, or '*'.
The condition can also be a table, with fields 'fields' (comma-sep string or table), 'sort_by' (string) and 'where' (Lua expression string or function)Parameters:
data
: table produced by readcondn
: select string or tablecontext
: a list of tables to be searched when resolving functionsreturn_row
: if true, wrap the results in a row table
Returns:
-
an iterator over the specified fields
- filter (Q, infile, outfile, dont_fail)
-
Filter input using a query.
Parameters:
Q
: a query stringinfile
: filename or file-like objectoutfile
: filename or file-like objectdont_fail
: true if you want to return an error, not just fail