Optimize Column Widths for Shortest Table Length

No. You can also optimize your column width by changing the height of some rows. This is after you auto fit your column widths. Once you change your row heights, you can re-do the auto column widths to make the overall column widths shorter.

Select all the columns by highlighting them. Right click. Go to AutoFit > AutoFit to Contents.

Or, on the menu bar, click Table, then AutoFit, then AutoFit to Contents.

In LibreOffice Writer: Select all the columns, right click, and go to Column > Optimal width.

More information on this subject here: http://www.brighthub.com/computing/windows-platform/articles/17718.aspx#imgn_3

By table length, you could mean several things:

If this is excel and you are looking to auto-narrow your columns:

By double clicking the cell-edge gap (red circle in image), the column will be resized to fit the text in it. This will also work for rows (double click the gap between rows 2 and 3 or 3 and 4 etc..). To resize all columns at once - click the "select all" corner (blue circle) and then pick a column/row (any one will do)

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If this is word and you are looking to auto-narrow your columns in a table:

Right click your table, go to "Auto Fit" and pick one of the auto-fit table options. You can also only narrow a single column by selecting a single column, editing the table properties, selecting the "column tab" and unticking the "Preferred Width" tick box:

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I could do this for other Office products - but if you want advice on a specific product, I need a specific product to give you a guide for!