torch.find works with 2D tensors

README.md

@@ -29,15 +29,31 @@ Example:
 ```
 
 <a name='torch.find'/>
-### [res] torch.find(tensor, val) ###
+### [res] torch.find(tensor, val, [dim]) ###
 Finds all indices of a given value `val` in Tensor `tensor`. 
-Returns a table of these indices.
+Returns a table of these indices by traversing the tensor one row 
+at a time. When `dim=2`, the only valid value for dim other than `nil` (the default),
+the function expects a matrix and returns the row-wise indices of each found 
+value `val` in the row.
 
-Example:
+1D example:
 ```lua
 > res = torch.find(torch.Tensor{1,2,3,1,1,2}, 1)
-> print(unpack(res))
- 1, 4, 5
+> unpack(res)
+1  4  5
+```
+
+2D example:
+```
+> tensor = torch.Tensor{{1,2,3,4,5},{5,6,0.6,0,2}}
+> unpack(torch.find(tensor, 2))
+2	10	
+> unpack(torch.find(tensor:t(), 2))
+3	10	
+> unpack(torch.find(tensor, 2, 2))
+{2}  {5}
+> unpack(torch.find(tensor:t(), 2, 2))
+{ }  {1}  { }  { }  {2}
 ```
 
 <a name='torch.group'/>

find.lua

@@ -1,22 +1,34 @@
 
 
-function torch.find(tensor, val)
-   if not torch.isTensor(tensor) then
-      asTable = val
-      val = tensor
-      tensor = res
-      if not asTable then
-         res = torch.LongTensor()
-      end
-   end
+function torch.find(tensor, val, dim)
    local i = 1
    local indice = {}
-   tensor:apply(function(x)
+   if dim then
+      assert(tensor:dim() == 2, "torch.find dim arg only supports matrices for now")
+      assert(dim == 2, "torch.find only supports dim=2 for now")
+
+      local colSize, rowSize = tensor:size(1), tensor:size(2)
+      local rowIndice = {}
+      tensor:apply(function(x)
+            if x == val then
+               table.insert(rowIndice, i)
+            end
+            if i == rowSize then
+               i = 1
+               table.insert(indice, rowIndice)
+               rowIndice = {}
+            else
+               i = i + 1
+            end
+         end)
+   else
+      tensor:apply(function(x)
          if x == val then
             table.insert(indice, i)
          end
          i = i + 1
       end)
+   end
    return indice
 end
 

test/test.lua

@@ -24,16 +24,18 @@ end
 
 function torchxtest.find()
    local tensor = torch.Tensor{1,2,3,4,5,6,0.6,0,2}
-   local indice = torch.find(tensor, 2)
-   mytester:assertTensorEq(indice, torch.LongTensor{2,9}, 0.00001, "find err")
-
-   indice = indice.new()
-   indice:find(tensor, 2)
-   mytester:assertTensorEq(indice, torch.LongTensor{2,9}, 0.00001, "find err")
+   local indice = torch.LongTensor(torch.find(tensor, 2))
+   mytester:assertTensorEq(indice, torch.LongTensor{2,9}, 0.00001, "find (1D) err")
 
-   local indiceTbl = torch.find(tensor, 2, true)
-   mytester:assert(torch.type(indiceTbl) == 'table', "find asTable type error")
-   mytester:assertTensorEq(indice, torch.LongTensor(indiceTbl), 0.00001, "find asTable value err")
+   local tensor = torch.Tensor{{1,2,3,4,5},{5,6,0.6,0,2}}
+   local indice = torch.find(tensor, 2)
+   mytester:assertTableEq(indice, {2,10}, 0.00001, "find (2D) err")
+   local indice = torch.find(tensor:t(), 2)
+   mytester:assertTableEq(indice, {3,10}, 0.00001, "find (2D transpose) err A")
+   local indice = torch.find(tensor:t(), 5)
+   mytester:assertTableEq(indice, {2,9}, 0.00001, "find (2D transpose) err B")
+   local indice = torch.find(tensor, 2, 2)
+   mytester:assertTableEq(indice, {{2},{5}}, 0.00001, "find (2D row-wise) err")
 end
 
 function torchxtest.remap()