Support header-less encoding.

README.md

@@ -200,6 +200,15 @@ file:close()
   --> ]]
   ```
 
+- `headers`
+
+If set to `false` it only outputs the data without the headers. This is useful
+for streaming CSV in chunks, by outputting the header first (e.g., using an
+empty table), and then one or more rows of data in a loop.
+
+To ensure a correct data layout, this option must be used with `fieldsToKeep`
+set to a constant ordering throughout the loop.
+
 ## Error Handling
 ftcsv returns a litany of errors when passed a bad csv file or incorrect parameters. You can find a more detailed explanation of the more cryptic errors in [ERRORS.md](ERRORS.md)
 

ftcsv.lua

@@ -828,8 +828,21 @@ function ftcsv.encode(inputTable, delimiter, options)
     local delimiter, options = determineArgumentOrder(delimiter, options)
     local output, headers = initializeGenerator(inputTable, delimiter, options)
 
+    local offset
+    if (options or {}).headers == false then
+        if #(options.fieldsToKeep or {}) == 0 then
+            error(
+                "`fieldsToKeep` must be specified if generating a CSV " ..
+                "without a header."
+            )
+        end
+        output = {}
+        offset = 0
+    else offset = 1 end
+
     for i, line in csvLineGenerator(inputTable, delimiter, headers, options) do
-        output[i+1] = line
+        -- Overwrite header with first line if headers is false
+        output[i + offset] = line
     end
 
     -- combine and return final string

spec/csvs/no_header.csv

@@ -0,0 +1,5 @@
+"E350",3000.00,1997
+"Venture ""Extended Edition""",4900.00,1999
+"Grand Cherokee",4799.00,1996
+"Venture ""Extended Edition, Very Large""",5000.00,1999
+"Venture ""Extended Edition""",4900.00,

spec/parse_encode_spec.lua

@@ -128,3 +128,20 @@ describe("csv encode with missing keys", function()
 		assert.are.same(jsonDecode, reEncoded)
 	end)
 end)
+
+
+describe("csv encode with selective omissions", function()
+	local jsonFile = loadFile("spec/json/correctness.json")
+	local jsonDecode = cjson.decode(jsonFile)
+
+	it("should output only data in a specific order", function()
+		local reEncoded = ftcsv.parse(ftcsv.encode(
+			jsonDecode, ",", {
+				fieldsToKeep = {"Model", "Price", "Year"},
+				headers = false,
+			}
+		), ",", {loadFromString=true, headers=false})
+		local exp = ftcsv.parse("spec/csvs/no_header.csv", {headers = false})
+		assert.are.same(exp, reEncoded)
+	end)
+end)