Text Data Processing

Delimited Field

Pick a Column

For small fixed examples, index and slices can split a delimited line without adding a parser dependency.

Program

Play the program to choose which comma-separated field is copied into field.

field_no
delimited_field.f90
Replay: real traced execution (multi-file project)
program delimited_field_demo
    implicit none
    integer :: field_no
    integer :: first_comma, second_comma
    character(len=20) :: line
    character(len=8) :: field

    field_no = 2
    line = 'red,green,blue'
    first_comma = index(line, ',')
    second_comma = first_comma + index(line(first_comma + 1:), ',')
    select case (field_no)
        case (1)
            field = line(1:first_comma - 1)
        case (2)
            field = line(first_comma + 1:second_comma - 1)
        case default
            field = line(second_comma + 1:len_trim(line))
    end select
    print '(A)', trim(field)
end program delimited_field_demo

program delimited_field_demo
    implicit none
    integer :: field_no
    integer :: first_comma, second_comma
    character(len=20) :: line
    character(len=8) :: field

    field_no = 1
    line = 'red,green,blue'
    first_comma = index(line, ',')
    second_comma = first_comma + index(line(first_comma + 1:), ',')
    select case (field_no)
        case (1)
            field = line(1:first_comma - 1)
        case (2)
            field = line(first_comma + 1:second_comma - 1)
        case default
            field = line(second_comma + 1:len_trim(line))
    end select
    print '(A)', trim(field)
end program delimited_field_demo

program delimited_field_demo
    implicit none
    integer :: field_no
    integer :: first_comma, second_comma
    character(len=20) :: line
    character(len=8) :: field

    field_no = 3
    line = 'red,green,blue'
    first_comma = index(line, ',')
    second_comma = first_comma + index(line(first_comma + 1:), ',')
    select case (field_no)
        case (1)
            field = line(1:first_comma - 1)
        case (2)
            field = line(first_comma + 1:second_comma - 1)
        case default
            field = line(second_comma + 1:len_trim(line))
    end select
    print '(A)', trim(field)
end program delimited_field_demo

  1. field_no ← 2

    8field_no = 29line = 'red,green,blue'
    values this step2field_no

  2. line ← red,green,blue

    8field_no = 29line = 'red,green,blue'10first_comma = index(line, ',')
    values this stepred,green,blueline

  3. first_comma ← 4

    9line = 'red,green,blue'10first_comma = index(line, ',')11second_comma = first_comma + index(line(first_comma + 1:), ',')
    values this step4first_commared,green,blueline

  4. second_comma ← 10

    10first_comma = index(line, ',')11second_comma = first_comma + index(line(first_comma + 1:), ',')12select case (field_no)
    values this step10second_comma4first_comma

  5. matched ← case (2)

    11second_comma = first_comma + index(line(first_comma + 1:), ',')12select case (field_no)13    case (1)
    values this stepcase (2)matched2field_no

  6. field ← green

    15case (2)16    field = line(first_comma + 1:second_comma - 1)17case default
    values this stepgreenfield

  7. print '(A)', trim(field)

    19    end select20    print '(A)', trim(field)21end program delimited_field_demo
    outputgreen
    values this stepgreenfield

  1. field_no ← 1

    8field_no = 19line = 'red,green,blue'
    values this step1field_no

  2. line ← red,green,blue

    8field_no = 19line = 'red,green,blue'10first_comma = index(line, ',')
    values this stepred,green,blueline

  3. first_comma ← 4

    9line = 'red,green,blue'10first_comma = index(line, ',')11second_comma = first_comma + index(line(first_comma + 1:), ',')
    values this step4first_commared,green,blueline

  4. second_comma ← 10

    10first_comma = index(line, ',')11second_comma = first_comma + index(line(first_comma + 1:), ',')12select case (field_no)
    values this step10second_comma4first_comma

  5. matched ← case (1)

    11second_comma = first_comma + index(line(first_comma + 1:), ',')12select case (field_no)13    case (1)
    values this stepcase (1)matched1field_no

  6. field ← red

    13case (1)14    field = line(1:first_comma - 1)15case (2)
    values this stepredfield

  7. print '(A)', trim(field)

    19    end select20    print '(A)', trim(field)21end program delimited_field_demo
    outputred
    values this stepredfield

  1. field_no ← 3

    8field_no = 39line = 'red,green,blue'
    values this step3field_no

  2. line ← red,green,blue

    8field_no = 39line = 'red,green,blue'10first_comma = index(line, ',')
    values this stepred,green,blueline

  3. first_comma ← 4

    9line = 'red,green,blue'10first_comma = index(line, ',')11second_comma = first_comma + index(line(first_comma + 1:), ',')
    values this step4first_commared,green,blueline

  4. second_comma ← 10

    10first_comma = index(line, ',')11second_comma = first_comma + index(line(first_comma + 1:), ',')12select case (field_no)
    values this step10second_comma4first_comma

  5. matched ← case default

    11second_comma = first_comma + index(line(first_comma + 1:), ',')12select case (field_no)13    case (1)
    values this stepcase defaultmatched3field_no

  6. field ← blue

    17    case default18        field = line(second_comma + 1:len_trim(line))19end select
    values this stepbluefield

  7. print '(A)', trim(field)

    19    end select20    print '(A)', trim(field)21end program delimited_field_demo
    outputblue
    values this stepbluefield
index `index(line, ',')` finds the position of a delimiter.
slice `line(first:last)` extracts a character section.
select case `select case` chooses the field-copy rule for this small example.