Add -select-column(s)

README.md

@@ -103,6 +103,8 @@ Functions returning a sublist of the original list.
 * [-take-while](#-take-while-pred-list) `(pred list)`
 * [-drop-while](#-drop-while-pred-list) `(pred list)`
 * [-select-by-indices](#-select-by-indices-indices-list) `(indices list)`
+* [-select-columns](#-select-columns-columns-table) `(columns table)`
+* [-select-column](#-select-column-column-table) `(column table)`
 
 ### List to list
 
@@ -575,6 +577,39 @@ as `(nth i list)` for all i from `indices`.
 (-select-by-indices '(0 1 2 0 1 3 3 1) '("f" "a" "r" "l")) ;; => '("f" "a" "r" "f" "a" "l" "l" "a")
 ```
 
+#### -select-columns `(columns table)`
+
+Select `columns` from `table`.
+
+`table` is a list of lists where each element represents one row.
+It is assumed each row has the same length.
+
+Each row is transformed such that only the specified `columns` are
+selected.
+
+See also: [`-select-column`](#-select-column-column-table), [`-select-by-indices`](#-select-by-indices-indices-list)
+
+```el
+(-select-columns '(0 2) '((1 2 3) (a b c) (:a :b :c))) ;; => '((1 3) (a c) (:a :c))
+(-select-columns '(1) '((1 2 3) (a b c) (:a :b :c))) ;; => '((2) (b) (:b))
+(-select-columns nil '((1 2 3) (a b c) (:a :b :c))) ;; => '(nil nil nil)
+```
+
+#### -select-column `(column table)`
+
+Select `column` from `table`.
+
+`table` is a list of lists where each element represents one row.
+It is assumed each row has the same length.
+
+The single selected column is returned as a list.
+
+See also: [`-select-columns`](#-select-columns-columns-table), [`-select-by-indices`](#-select-by-indices-indices-list)
+
+```el
+(-select-column 1 '((1 2 3) (a b c) (:a :b :c))) ;; => '(2 b :b)
+```
+
 
 ## List to list
 

dash.el

@@ -1189,6 +1189,29 @@ as `(nth i list)` for all i from INDICES."
       (!cons (nth it list) r))
     (nreverse r)))
 
+(defun -select-columns (columns table)
+  "Select COLUMNS from TABLE.
+
+TABLE is a list of lists where each element represents one row.
+It is assumed each row has the same length.
+
+Each row is transformed such that only the specified COLUMNS are
+selected.
+
+See also: `-select-column', `-select-by-indices'"
+  (--map (-select-by-indices columns it) table))
+
+(defun -select-column (column table)
+  "Select COLUMN from TABLE.
+
+TABLE is a list of lists where each element represents one row.
+It is assumed each row has the same length.
+
+The single selected column is returned as a list.
+
+See also: `-select-columns', `-select-by-indices'"
+  (--mapcat (-select-by-indices (list column) it) table))
+
 (defmacro -> (x &optional form &rest more)
   "Thread the expr through the forms. Insert X as the second item
 in the first form, making a list of it if it is not a list
@@ -2341,6 +2364,8 @@ structure such as plist or alist."
                              "-find-last-index"
                              "--find-last-index"
                              "-select-by-indices"
+                             "-select-columns"
+                             "-select-column"
                              "-grade-up"
                              "-grade-down"
                              "->"

dev/examples.el

@@ -179,7 +179,15 @@ new list."
   (defexamples -select-by-indices
     (-select-by-indices '(4 10 2 3 6) '("v" "e" "l" "o" "c" "i" "r" "a" "p" "t" "o" "r")) => '("c" "o" "l" "o" "r")
     (-select-by-indices '(2 1 0) '("a" "b" "c")) => '("c" "b" "a")
-    (-select-by-indices '(0 1 2 0 1 3 3 1) '("f" "a" "r" "l")) => '("f" "a" "r" "f" "a" "l" "l" "a")))
+    (-select-by-indices '(0 1 2 0 1 3 3 1) '("f" "a" "r" "l")) => '("f" "a" "r" "f" "a" "l" "l" "a"))
+
+  (defexamples -select-columns
+    (-select-columns '(0 2) '((1 2 3) (a b c) (:a :b :c))) => '((1 3) (a c) (:a :c))
+    (-select-columns '(1) '((1 2 3) (a b c) (:a :b :c))) => '((2) (b) (:b))
+    (-select-columns nil '((1 2 3) (a b c) (:a :b :c))) => '(nil nil nil))
+
+  (defexamples -select-column
+    (-select-column 1 '((1 2 3) (a b c) (:a :b :c))) => '(2 b :b)))
 
 (def-example-group "List to list"
   "Bag of various functions which modify input list."