2 Incorporated J.M.'s comment into the answer
source | link

You can try Tally

lst = {"aa bb", "cc dd", "aa bb", "aa bb", "cc dd", "ww ss", "ss ss",   "kk mm"};
Tally[lst]

Mathematica graphics

Edit by m_goldberg

As J.M. says in his comment below, Counts will give the same information as an association.

Counts[data]

<|"aa bb" -> 3, "cc dd" -> 2, "ww ss" -> 1, "ss ss" -> 1, "kk mm" -> 1|>

This is equivalent to

Rule @@@ Tally[data] // Association

You can try Tally

lst = {"aa bb", "cc dd", "aa bb", "aa bb", "cc dd", "ww ss", "ss ss",   "kk mm"};
Tally[lst]

Mathematica graphics

You can try Tally

lst = {"aa bb", "cc dd", "aa bb", "aa bb", "cc dd", "ww ss", "ss ss",   "kk mm"};
Tally[lst]

Mathematica graphics

Edit by m_goldberg

As J.M. says in his comment below, Counts will give the same information as an association.

Counts[data]

<|"aa bb" -> 3, "cc dd" -> 2, "ww ss" -> 1, "ss ss" -> 1, "kk mm" -> 1|>

This is equivalent to

Rule @@@ Tally[data] // Association
1
source | link

You can try Tally

lst = {"aa bb", "cc dd", "aa bb", "aa bb", "cc dd", "ww ss", "ss ss",   "kk mm"};
Tally[lst]

Mathematica graphics