Pick out elements wherever a 1 appears in the "selector" list:

Pick out elements from a 2D array:

Pick out elements wherever True appears in the "selector" list:

Pick elements whose parts match a pattern:

Use a SparseArray to select arguments:

Pick elements from a SparseArray:

Create a data structure of type "BitVector" and length five:

Set its second and fourth bits to 1, cognizant of the fact that it is 0-indexed rather than 1-indexed:

Extract those elements of a list using the data structure:

The data does not have to be a list:

The selector argument need not be a list:

Convert strings to a list of characters to pick only certain characters:

Use Pick with a normal list of True and False:

The same operation using the corresponding DataStructure is much faster:

The results are the same:

The comparison in Pick[list,sel,patt] is purely structural, with no regard to heads:

f[b] is selected because the 3,1 part of sel matches the patt:

The corresponding part of list, if it exists, will be picked, along with its heads:

Note that the 2,1 part of sel also matches patt:

However, there is no corresponding part of list to be picked:

Compute Pick in parallel:

If sel is a bit vector, Pick[list,sel] retrieves the elements of list corresponding to the value 1 in sel:

The "selector" list has to have the same length and structure as the data:

Atomic expressions are allowed in Pick:

This is because all parts—including the empty part—are tested for matching:

If there is an atomic argument and it is not picked in its entirety, Sequence[] is returned:

This applies equally to the second argument:

Using Except[c] in the third argument can lead to unexpected results:

The whole expression is returned because the entire selector argument matches the pattern:

Use Except[c,p] to restrict the pattern to elements of the selector argument:

Using nonatomic expressions in the selector argument can lead to unexpected results:

Applying the test beforehand so the list only contains True and False avoids the structure issue: