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Add slice function #250

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merged 2 commits into from
Apr 21, 2015
Merged

Add slice function #250

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7210ac7
Add slice function
megawac Mar 19, 2015
9e6c4f6
Handling of negative indicies in slice
megawac Apr 17, 2015
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84 changes: 42 additions & 42 deletions lib/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2381,45 +2381,63 @@ Stream.prototype.split = function () {
exposeMethod('split');

/**
* Creates a new Stream with the first `n` values from the source.
* Creates a new Stream with the values from the source in the range of `start` to `end`.
*
* @id take
* @id slice
* @section Transforms
* @name Stream.take(n)
* @param {Number} n - integer representing number of values to read from source
* @name Stream.slice(start, end)
* @param {Number} start - integer representing index to start reading from source
* @param {Number} stop - integer representing index to stop reading from source
* @api public
*
* _([1, 2, 3, 4]).take(2) // => 1, 2
* _([1, 2, 3, 4]).slice(1, 3) // => 2, 3
*/

Stream.prototype.take = function (n) {
if (n === 0) {
Stream.prototype.slice = function(start, end) {
var index = 0;
start = typeof start != 'number' || start < 0 ? 0 : start;
end = typeof end != 'number' ? Infinity : end;

if (start === 0 && end === Infinity) {
return this;
} else if (start >= end) {
return _([]);
}
var s = this.consume(function (err, x, push, next) {
var done = x === nil;
if (err) {
push(err);
if (n > 0) {
next();
}
else {
push(null, nil);
}
}
else if (x === nil) {
push(null, nil);
else if (!done && index++ >= start) {
push(null, x);
}

if (!done && index < end) {
next();
}
else {
n--;
push(null, x);
if (n > 0) {
next();
}
else {
push(null, nil);
}
push(null, nil);
}
});
s.id = 'slice:' + s.id;
return s;
};
exposeMethod('slice');

/**
* Creates a new Stream with the first `n` values from the source.
*
* @id take
* @section Transforms
* @name Stream.take(n)
* @param {Number} n - integer representing number of values to read from source
* @api public
*
* _([1, 2, 3, 4]).take(2) // => 1, 2
*/

Stream.prototype.take = function (n) {
var s = this.slice(0, n);
s.id = 'take:' + s.id;
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Is this stuff important?

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The s.id? No. It's mostly for debugging. No harm in leaving it though.

return s;
};
Expand All @@ -2440,25 +2458,7 @@ exposeMethod('take');
*/

Stream.prototype.drop = function (n) {
if (n <= 0) {
return this;
}
return this.consume(function (err, x, push, next) {
if (err) {
push(err);
next();
}
else if (x === nil) {
push(null, nil);
}
else {
n--;
if (n < 0) {
push(null, x);
}
next();
}
});
return this.slice(n, Infinity);
};
exposeMethod('drop');

Expand Down
54 changes: 54 additions & 0 deletions test/test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -949,6 +949,55 @@ exports['take'] = function (test) {
test.done();
};

exports['slice'] = {
setUp: function (cb) {
this.input = [1, 2, 3, 4, 5];
this.expected = [3, 4, 5];
this.tester = function (expected, test) {
return function (xs) {
test.same(xs, expected);
};
};
cb();
},
'arrayStream': function (test) {
test.expect(5);
_(this.input).slice(2, 6).toArray(this.tester(this.expected, test));
_(this.input).slice(2).toArray(this.tester(this.expected, test));
_(this.input).slice().toArray(this.tester(this.input, test));
_(this.input).slice(-1, 6).toArray(this.tester(this.input, test));
_(this.input).slice(0).toArray(this.tester(this.input, test));
test.done();
},
'partial application': function (test) {
test.expect(1);
var s = _(this.input);
_.slice(1, 4)(s).toArray(this.tester([2, 3, 4], test));
test.done();
},
'negative indicies': function(test) {
test.expect(1);
_.slice(-5, Infinity)(this.input).toArray(this.tester(this.input, test));
test.done();
},
'error': function (test) {
test.expect(2);
var s = _(function (push, next) {
push(null, 1),
push(new Error('Slice error')),
push(null, 2),
push(null, 3),
push(null, 4),
push(null, 5),
push(null, _.nil)
});
s.slice(2, 4).errors(errorEquals(test, 'Slice error'))
.toArray(this.tester([3, 4], test));
test.done();
},
'noValueOnError': noValueOnErrorTest(_.slice(2, 3))
};

exports['take - noValueOnError'] = noValueOnErrorTest(_.take(1));

exports['take - errors'] = function (test) {
Expand Down Expand Up @@ -1010,6 +1059,11 @@ exports['drop'] = {
_.drop(2)(s).toArray(this.tester(this.expected, test));
test.done();
},
'negative indicies': function(test) {
test.expect(1);
_.drop(-1)(this.input).toArray(this.tester(this.input, test));
test.done();
},
'error': function (test) {
test.expect(2);
var s = _(function (push, next) {
Expand Down