Returns the contents of a cell either from a one-row or one-column range. Optionally, the assigned value (of the same index) is returned in a different column and row. As opposed to VLOOKUP and HLOOKUP, search and result vector may be at different positions; they do not have to be adjacent. Additionally, the search vector for the LOOKUP must be sorted ascending, otherwise the search will not return any usable results.
LOOKUP(SearchCriterion; SearchVector; ResultVector)
SearchCriterion is the value to be searched for; entered either directly or as a reference.
SearchVector is the single-row or single-column area to be searched.
ResultVector is another single-row or single-column range from which the result of the function is taken. The result is the cell of the result vector with the same index as the instance found in the search vector.
If LOOKUP cannot find the search criterion, it matches the largest value in the search vector that is less than or equal to the search criterion.
The search supports wildcards or regular expressions. With regular expressions enabled, you can enter "all.*", for example to find the first location of "all" followed by any characters. If you want to search for a text that is also a regular expression, you must either precede every character with a "\" character, or enclose the text into \Q...\E. You can switch the automatic evaluation of wildcards or regular expression on and off in Tools - Options - LibreOffice Calc - Calculate.
When using functions where one or more arguments are search criteria strings that represents a regular expression, the first attempt is to convert the string criteria to numbers. For example, ".0" will convert to 0.0 and so on. If successful, the match will not be a regular expression match but a numeric match. However, when switching to a locale where the decimal separator is not the dot makes the regular expression conversion work. To force the evaluation of the regular expression instead of a numeric expression, use some expression that can not be misread as numeric, such as "." or ".\0" or "(?i).0".
See Help article entitled Handling of Empty Cells.
=LOOKUP(A1;D1:D100;F1:F100) searches the corresponding cell in range D1:D100 for the number you entered in A1. For the instance found, the index is determined, for example, the 12th cell in this range. Then, the contents of the 12th cell are returned as the value of the function (in the result vector).