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[stdlib] Add std.flatMap #752

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Merged
sbarzowski merged 1 commit into from
Dec 30, 2019
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[stdlib] Add std.flatMap #752

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28 changes: 28 additions & 0 deletions doc/ref/stdlib.html
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Expand Up @@ -1399,6 +1399,34 @@ <h4 id="filterMap">std.filterMap(filter_func, map_func, arr)</h4>
</div>
</div>

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<h4 id="flatMap">std.flatMap(func, arr)</h4>
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<div style="clear: both"></div>
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</div>

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<p>Apply the given function to every element of the array to form a new array then flatten the result.
It can be thought of as a generalized map, where each element can get mapped to 0, 1 or more elements.
</p>
<p>
Example: <code>std.flatMap(function(x) [x, x], [1, 2, 3])</code> yields <code>[1, 1, 2, 2, 3, 3])</code>.
</p>
<p>
Example: <code>std.flatMap(function(x) if x == 2 then [] else [x], [1, 2, 3])</code> yields <code>[1, 3])</code>.
</p>
<p>
Example: <code>std.flatMap(function(x) if x == 2 then [] else [x * 3, x * 2], [1, 2, 3])</code> yields <code>[3, 2, 9, 6])</code>.
</p>
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<div style="clear: both"></div>
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9 changes: 9 additions & 0 deletions stdlib/std.jsonnet
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Expand Up @@ -259,6 +259,15 @@ limitations under the License.
else
{ [k]: func(k, obj[k]) for k in std.objectFields(obj) },

flatMap(func, arr)::
if std.type(func) != 'function' then
error ('std.flatMap first param must be function, got ' + std.type(func))
else if std.isArray(arr) then
std.flattenArrays(std.makeArray(std.length(arr), function(i) func(arr[i])))
else if std.isString(arr) then
std.join('', std.makeArray(std.length(arr), function(i) func(arr[i])))
else error ('std.flatMap second param must be array / string, got ' + std.type(arr)),

join(sep, arr)::
local aux(arr, i, first, running) =
if i >= std.length(arr) then
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4 changes: 4 additions & 0 deletions test_suite/stdlib.jsonnet
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Expand Up @@ -202,6 +202,10 @@ std.assertEqual(std.mapWithIndex(function(i, x) x * i, std.filter(function(x) x
std.assertEqual(std.mapWithKey(function(k, o) k + o, {}), {}) &&
std.assertEqual(std.mapWithKey(function(k, o) k + o, { a: 1, b: 2 }), { a: 'a1', b: 'b2' }) &&

std.assertEqual(std.flatMap(function(x) [x, x], [1, 2, 3]), [1, 1, 2, 2, 3, 3]) &&
std.assertEqual(std.flatMap(function(x) if x == 2 then [] else [x], [1, 2, 3]), [1, 3]) &&
std.assertEqual(std.flatMap(function(x) if x == 2 then [] else [x * 3, x * 2], [1, 2, 3]), [3, 2, 9, 6]) &&

std.assertEqual(std.filterMap(function(x) x >= 0, function(x) x * x, [-3, -2, -1, 0, 1, 2, 3]), [0, 1, 4, 9]) &&

std.assertEqual(std.foldl(function(x, y) [x, y], [], 'foo'), 'foo') &&
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