# compare-list command

The compare-list BASIC program forms
a single list from two lists using the intersection, union, or exclusion
operators.

## Syntax

```
compare-list {file.reference.a}lista operator{file.reference.b}
listb{file.reference.c} {listc} {(options)}
```
or, if the primary and secondary lists are already active:

```
compare-list operator{listc}{(options}
```

## Parameter(s)

| file.reference.a | File that contains the list specified in ista. | |
| --- | --- | --- |
| lista | First list. CAUTION: This argument will be treated as a filename first, then as a listname. Thus, if a file with the same name as the listname (specified in lista) exists in the file specified in file.reference.a, an error will occur. | |
| file.reference.b | File that contains the list specified in listb. | |
| listb | Second list. CAUTION: This argument will be treated as a filename first, then as a listname. Thus, if a file with the same name as the listname (specified in listb) exists in the file specified in file.reference.b, an error will occur. | |
| file.reference.c | File that contains the list specified in listc. | |
| listc | Third list. CAUTION: This argument will be treated as a filename first, then as a listname. Thus, if a file with the same name as the listname (specified in listc) exists in the file specified in file.reference.c, an error will occur. | |
| operators | & | Represents an and or intersection, which means that the item-IDs must exist in both lists. |
| # | Represents a not or exclusion, which means that the item IDs must not exist in both lists. | |
| = | Represents an or union, indicating that the item-IDs can exist in either list. | |
| + | Concatenates listb to the end of lista. For example: lista + listb | |
| - | Removes item-IDs in listb from lista. For example: lista - listb | |
| options | g | Performs a get-list on listc. For example, makes listc active after the process. |
| s | Generates and displays statistics about the items selected during the process. If this option is not used, no message displays. | |
Note: The ? displays the help text on
screen.

The compare-list command performs
the operation (&, #, =, +, or `-`) on *lista* and *listb* and creates a new list, *listc*. If *listc* is not specified, it
overwrites *lista*.

## Example(s)

Assume that these two lists below
are already created and reside in the pointer-file file.

| list1 | list2 |
| --- | --- |
| 001 cat | 001 banana |
| 002 dog | 002 apple |
| 003 banana | 003 orange |
Since no *listc* was specified, `list1` is overwritten and contains banana, cat, dog, apple,
banana, and orange.

```
compare-list list1 + list2
```
This example is exactly the same as the first example,
but the list is saved as `list3`. `list1` and `list2` remain unchanged.

```
compare-list list1 + list2 list3
```
Creates a `list3`, which contains apple,
cat, dog, and orange, since none of these display in both `list1` and `list2`. `list1` and `list2` remain unchanged.

```
compare-list list1 # list2 list3
```
Creates and activates `list3`, which contains
apple, banana, cat, dog, and orange, or all unique strings in both `list1` and `list2`. `list1` and `list2` remain unchanged.

```
compare-list list1 = list2 list3 (gs
list2 list1 list3 Sort time - faster than a speeding second.
3 3 5 Duty time - faster than a speeding second.
[404] 5 items selected out of 1 items.
```
Creates a `list3`, which contains cat and dog. Those strings, which
exist in `list2` (banana, in this case) are removed
from `list1`. `list1` and `list2` remain unchanged.

```
compare-list list1 - list2 list3
```
Creates a `list3`, which contains banana,
since it is the only string, which displays in both `list1` and `list2`. `list1` and `list2` remain unchanged.

```
compare-list list1 & list2 list3
```

## See also

- [Active list](https://d3codex.com/definitions/active-list/)
- [compare command](https://d3codex.com/tcl/compare-command/)
- [copy-list command](https://d3codex.com/tcl/copy-list-command/)
- [delete-list command](https://d3codex.com/tcl/delete-list-command/)
- [edit-list command](https://d3codex.com/tcl/edit-list-command/)
- [fl command](https://d3codex.com/tcl/fl-command/)
- [get-list command](https://d3codex.com/tcl/get-list-command/)
- [nselect command](https://d3codex.com/access/nselect-command/)
- [Primary list](https://d3codex.com/definitions/primary-list/)
- [save-list command](https://d3codex.com/tcl/save-list-command/)
- [Secondary list](https://d3codex.com/definitions/secondary-list/)
- [nselect command](https://d3codex.com/access/nselect-command/)
- [sort-list command](https://d3codex.com/tcl/sort-list-command/)
- [sselect command](https://d3codex.com/access/sselect-command/)

---
Source: https://d3codex.com/tcl/compare-list-command/ - part of the D3Codex reference.