Add Get A Slice Of The Ends Of An Array as a jq TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1390 TILs and counting..._
+_1391 TILs and counting..._
 
 ---
 
@@ -528,6 +528,7 @@ _1390 TILs and counting..._
 - [Filter Out Results Based On List Of Values](jq/filter-out-results-based-on-list-of-values.md)
 - [Find All Objects In An Array Where Key Is Set](jq/find-all-objects-in-an-array-where-key-is-set.md)
 - [Find All Objects With A Matching Key Value Pair](jq/find-all-objects-with-a-matching-key-value-pair.md)
+- [Get A Slice Of The Ends Of An Array](jq/get-a-slice-of-the-ends-of-an-array.md)
 - [Get The First Item For Every Top-Level Key](jq/get-the-first-item-for-every-top-level-key.md)
 - [Get The Last Item From An Array](jq/get-the-last-item-from-an-array.md)
 - [Reduce Object To Just Entries Of A Specific Type](jq/reduce-object-to-just-entries-of-a-specific-type.md)

jq/get-a-slice-of-the-ends-of-an-array.md

@@ -0,0 +1,37 @@
+# Get A Slice Of The Ends Of An Array
+
+[`jq`](https://jqlang.github.io/jq/) has an array slice syntax that allows us
+to grab a subset of values from an array. The general form of this syntax is
+`[n:m]` where `n` is the index of the start of our slice (inclusive) and `m` is
+the index of the end of our slice (non-inclusive).
+
+If we omit the `n`, it defaults to `0`, or the start of the array. Similarly,
+if we omit the `m`, it defaults to the end of the list.
+
+Knowing that, we can grab the first few elements of the list like so:
+
+```bash
+❯ echo '["a","b","c","d","e","f","g"]' | jq '.[:3]'
+[
+  "a",
+  "b",
+  "c"
+]
+```
+
+We can also use a negative index value to count back from the end of the array.
+This allows us to grab a slice from some point relative to the end of the list.
+Instead of having to compute it based on knowing the length of the array.
+
+Knowing that, we can grab the last few elements of the list like so:
+
+```bash
+❯ echo '["a","b","c","d","e","f","g"]' | jq '.[-3:]'
+[
+  "e",
+  "f",
+  "g"
+]
+```
+
+[source](https://jqlang.github.io/jq/manual/#array-string-slice)