From b133cfb63421075671fb3033d0321b94a1a74bc4 Mon Sep 17 00:00:00 2001
From: Bhuvaneshwara Raja <bhuvaneshwara.raja@ei.study>
Date: Sun, 24 Sep 2023 20:55:35 +0530
Subject: [PATCH] Skip lines future (Feature Suggestion) #738

---
 docs/docs.html      | 11 ++++++++-
 papaparse.js        | 20 +++++++++++++++--
 player/player.html  |  1 +
 player/player.js    |  1 +
 tests/test-cases.js | 54 +++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 84 insertions(+), 3 deletions(-)

diff --git a/docs/docs.html b/docs/docs.html
index 49095b17..b9292fad 100644
--- a/docs/docs.html
+++ b/docs/docs.html
@@ -450,7 +450,8 @@ <h5 id="config-default">Default Config With All Options</h5>
 	beforeFirstChunk: undefined,
 	withCredentials: undefined,
 	transform: undefined,
-	delimitersToGuess: [',', '\t', '|', ';', <a href="#readonly">Papa.RECORD_SEP</a>, <a href="#readonly">Papa.UNIT_SEP</a>]
+	delimitersToGuess: [',', '\t', '|', ';', <a href="#readonly">Papa.RECORD_SEP</a>, <a href="#readonly">Papa.UNIT_SEP</a>],
+	skipFirstNLines: 0
 }</code></pre>
 					</div>
 					<div class="clear"></div>
@@ -682,6 +683,14 @@ <h5 id="config-details">Config Options</h5>
 									An array of delimiters to guess from if the <code>delimiter</code> option is not set.
 								</td>
 							</tr>
+							<tr>
+								<td>
+									<code>skipFirstNLines</code>
+								</td>
+								<td>
+									To skip first N number of lines when converting a CSV file to JSON 
+								</td>
+							</tr>
 						</table>
 					</div>
 				</div>
diff --git a/papaparse.js b/papaparse.js
index 3ce39621..ff110692 100755
--- a/papaparse.js
+++ b/papaparse.js
@@ -484,6 +484,10 @@ License: MIT
 		}
 	}
 
+	function customSplice(inputArray, startIndex, count) {
+		return [...inputArray.slice(0, startIndex), ...inputArray.slice(startIndex + count)];
+	}
+
 	/** ChunkStreamer is the base prototype for various streamer implementations. */
 	function ChunkStreamer(config)
 	{
@@ -519,8 +523,21 @@ License: MIT
 
 			// Rejoin the line we likely just split in two by chunking the file
 			var aggregate = this._partialLine + chunk;
+			this._skipLines = parseInt(this._config.skipFirstNLines) || 0;
+			this._pendingSkip = parseInt(this._config.skipFirstNLines) || 0;
+			this._skipHeader = this._config.header ? 1 : 0;
+			if (this._pendingSkip > 0 && this._pendingSkip <= this._skipLines) {
+				var splitChunk = aggregate.split('\n');
+				var currentChunkLength = splitChunk.length;
+				if (currentChunkLength <= this._pendingSkip) {
+					aggregate = this._partialLine;
+				}
+				else{
+					aggregate = this._partialLine + customSplice(splitChunk,this._skipHeader,this._pendingSkip).join('\n');
+				}
+				this._pendingSkip = this._skipLines - currentChunkLength;
+			}
 			this._partialLine = '';
-
 			var results = this._handle.parse(aggregate, this._baseIndex, !this._finished);
 
 			if (this._handle.paused() || this._handle.aborted()) {
@@ -1929,7 +1946,6 @@ License: MIT
 	{
 		return function() { f.apply(self, arguments); };
 	}
-
 	function isFunction(func)
 	{
 		return typeof func === 'function';
diff --git a/player/player.html b/player/player.html
index b90fe986..48015e35 100644
--- a/player/player.html
+++ b/player/player.html
@@ -24,6 +24,7 @@ <h1><a href="http://papaparse.com">Papa Parse</a> Player</h1>
 				<label><input type="checkbox" id="skipEmptyLines"> Skip empty lines</label>
 				<label><input type="checkbox" id="step-pause"> Pause on step</label>
 				<label><input type="checkbox" id="print-steps"> Log each step/chunk</label>
+				<label>Skip First N Lines: <input type="number" id="skipFirstNLines"></label>
 				
 				<label>Delimiter: <input type="text" size="5" placeholder="auto" id="delimiter"> <a href="javascript:" id="insert-tab">tab</a></label>
 
diff --git a/player/player.js b/player/player.js
index 8150de64..f8b8e3ac 100644
--- a/player/player.js
+++ b/player/player.js
@@ -108,6 +108,7 @@ function buildConfig()
 		skipEmptyLines: $('#skipEmptyLines').prop('checked'),
 		chunk: $('#chunk').prop('checked') ? chunkFn : undefined,
 		beforeFirstChunk: undefined,
+		skipFirstNLines: $('#skipFirstNLines').val()
 	};
 
 	function getLineEnding()
diff --git a/tests/test-cases.js b/tests/test-cases.js
index da489e8c..66a6f090 100644
--- a/tests/test-cases.js
+++ b/tests/test-cases.js
@@ -1574,6 +1574,60 @@ var PARSE_TESTS = [
 			data: [['a', 'b', 'c\n'], ['d', 'e', 'f']],
 			errors: []
 		}
+	},
+	{
+		description: "Skip First N number of lines , with header and 2 rows",
+		input: 'a,b,c,d\n1,2,3,4',
+		config: { header: true, skipFirstNLines: 1 },
+		expected: {
+			data: [],
+			errors: []
+		}
+	},
+	{
+		description: "Skip First N number of lines , with header and 3 rows",
+		input: 'a,b,c,d\n1,2,3,4\n4,5,6,7',
+		config: { header: true, skipFirstNLines: 1 },
+		expected: {
+			data: [{a: '4', b: '5', c: '6', d: '7'}],
+			errors: []
+		}
+	},
+	{
+		description: "Skip First N number of lines , with header false",
+		input: 'a,b,c,d\n1,2,3,4\n4,5,6,7',
+		config: { header: false, skipFirstNLines: 1 },
+		expected: {
+			data: [['1','2','3','4'],['4','5','6','7']],
+			errors: []
+		}
+	},
+	{
+		description: "Skip First N number of lines , with header false and skipFirstNLines as 0",
+		input: 'a,b,c,d\n1,2,3,4\n4,5,6,7',
+		config: { header: false, skipFirstNLines: 0 },
+		expected: {
+			data: [['a','b','c','d'],['1','2','3','4'],['4','5','6','7']],
+			errors: []
+		}
+	},
+	{
+		description: "Skip First N number of lines , with header false and skipFirstNLines as negative value",
+		input: 'a,b,c,d\n1,2,3,4\n4,5,6,7',
+		config: { header: false, skipFirstNLines: -2 },
+		expected: {
+			data: [['a','b','c','d'],['1','2','3','4'],['4','5','6','7']],
+			errors: []
+		}
+	},
+	{
+		description: "Without Skip First N number of lines",
+		input: 'a,b,c,d\n1,2,3,4\n4,5,6,7',
+		config: { header: false},
+		expected: {
+			data: [['a','b','c','d'],['1','2','3','4'],['4','5','6','7']],
+			errors: []
+		}
 	}
 ];