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Data extraction and reporting from multiple files
File and Directory Handling example from a Well House Consultants training course
More on File and Directory Handling [link]

This example is described in the following article(s):
   • Tcl - Some example of HOW TO in handling data files and formats - [link]

Source code: rail Module: T209

# Scenario. We have a number of (published, government) tables of the number of tickets sold for
# journeys to and from stations on the main railway network of Great Britain on an annual basis, but
# the format of the file for each year varies - fields have been added and removed, and any numbers
# over 999 have commas added to split up the numbers which is great for the human reader, but causes
# programs that want to further analyse the data some problems. We also have a file that include the
# location of stations in Ordnance Survey grid terms, postcode, latitude and longitude, etc.
#
# Our objective is to produce a single output file, one record per station, that includes fields for
# the station's details at the start, and then a total of the number of entrances and exits year by
# year.

# Define functions used in main program

# Add to a list, or add NULL if value does not exist

proc nappend {list value} {
        upvar $list target

        set there 0
        if {$value != ""} {
                set updo "info exists $value"
                catch {set there [uplevel $updo]} errst
        }

        if {$there} {
                upvar $value vn
                lappend target $vn
        } else {
                lappend target NULL
        }
}

# Sort by postocde, moving all unpostcoded records to the end

proc pcs {a b} {
        global postcode
        global tlctable

        set rv 0
        if {[catch {set at $postcode($tlctable($a))} errst]} {return 1}
        if {[catch {set bt $postcode($tlctable($b))} errst]} {return -1}

        return [string compare $at $bt]
        }

# -------- Main Program

# Definition of fields of interest in varying different annual file formats

set filespec {
        {{station_usage_0910.csv 2009 23} {four 0} {tlc 1} {name 2} {thisyear 21}}
        {{station_usage_0809.csv 2008 23} {four 0} {tlc 1} {name 2} {thisyear 21}}
        {{station_usage_0708.csv 2007 23} {four 0} {tlc 1} {name 2} {thisyear 16}}
        {{station_usage_0607.csv 2006 23} {four 0} {tlc 1} {name 2} {thisyear 16}}
        {{station_usage_0506.csv 2005 16} {four 4} {tlc 1} {name 0} {thisyear 13}}
        {{station_usage_0405.csv 2004 16} {four 4} {tlc 1} {name 0} {thisyear 13}}
        }

foreach year $filespec {

# read the format for the year

        set yeardata [lindex $year 0]
        set wanted [lrange $year 1 end]

        set filename [lindex $yeardata 0]
        set yearnumber [lindex $yeardata 1]
        set minfields [lindex $yeardata 2]

        set fh [open $filename r]

# read each record for the year

        while 1 {

                gets $fh record
                if {$record == ""} break
                set fields [split $record "\t"]

# Eliminate short (header and / or damaged) records

                if {[llength $fields] < $minfields} continue

# extract the fields that are wanted from the right columns for this year

                foreach pair $wanted {
                        set f_name [lindex $pair 0]
                        set f_col [lindex $pair 1]
                        set $f_name [lindex $fields $f_col]
                        }

# Substitute - decomma
                regsub -all , $thisyear "" thisyear
                regsub -all {"} $four "" four

# Extract - dequote
                regexp {"([[:alpha:]]{3})"} $tlc whole tlc

                regsub -all \" $name "" name
                if {[regexp ^....$ $four]} {
                        # if {$four == "3333"} {puts "$tlc $four $yearnumber $thisyear $name"}

# Save the passenger count for this station and year

                        set station_annual("$four/$yearnumber") $thisyear

# First time for this station - save name and three letter code
                        if {[info exists nametable($four)]} continue
                        set nametable($four) $name
                        set tlctable($four) $tlc
                }
        }
}

# --- At this point we have read in the data for each year
# Now read in the ancilliary data for each station

set fh [open stationtables.tsv r]
while {[gets $fh line] >= 0} {
        set fields [split $line "\t"]
        set tlc [lindex $fields 0]

        set osgrid($tlc) [lindex $fields end]
        set postcode($tlc) [lindex $fields 2]
        set lat($tlc) [lindex $fields 3]
        set long($tlc) [lindex $fields 4]
}

# Generate output file; get station order first

set fho [open railstats.txt w]

set tlcs [array names tlctable]
set tlcs [lsort -command pcs $tlcs]

foreach station $tlcs {
        set tlc $tlctable($station)

# Initial fields on each line

        set line ""
        nappend line station
        nappend line tlc
        nappend line postcode($tlc)
        nappend line osgrid($tlc)
        nappend line lat($tlc)
        nappend line long($tlc)
        nappend line nametable($station)

# Add annual data

        foreach yearnumber {2004 2005 2006 2007 2008 2009} {
                nappend line station_annual("$station/$yearnumber")
        }

# Fields in output record:

# 1 - 4 digit station code
# 2 - Three letter code for station
# 3 - Station's postcode
# 4 - OS grid reference for station
# 5 - Latitude of station
# 6 - Longitude of station
# 7 - Station name
# 8 - Ticket sales - April 2004 - March 2005 for joureys to / from this station
# 9 - Ticker sales, April 2005 to March 2006
# 10 - Ticker sales, April 2006 to March 2007
# 11 - Ticker sales, April 2005 to March 2008
# 12 - Ticker sales, April 2008 to March 2009
# 13 - Ticker sales, April 2009 to March 2010
#
# 14 - April 2010 to March 2011 (added via Perl, 29.3.2012)

# Turn into tab delimited line

        set newline [join $line "\t"]

# Output the record provided that there are no problems with it

        if {[regexp "^...$" $tlc]} {
                puts $fho $newline
        } else {
                puts $newline
        }

}

Learn about this subject
This module and example are covered on the following public courses:
 * Learning to program in Tcl
 * Tcl Programming
 * Tcl Programming
Also available on on site courses for larger groups

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Other Examples
This example comes from our "File and Directory Handling" training module. You'll find a description of the topic and some other closely related examples on the "File and Directory Handling" module index page.

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