Selectively replace multiple instances of a character within a string: Difference between revisions

Content added Content deleted

Inline

@@ Line 512: / Line 512: @@
         ],
     )
+)</lang>
-)
-</lang>
 {{out}}
-<pre>
+<pre>AErBcadCbFD</pre>
-AErBcadCbFD
-</pre>
+Or, as a map-accumulation:
+<lang python>from functools import reduce
+# nthInstanceReplaced :: Dict Char [(None | Char)] ->
+# String -> String
+def nthInstanceReplaced(ruleMap):
+    def go(a, c):
+        i = a.get(c, 0)
+        deltas = ruleMap.get(c, [])
+        return (
+            dict(a, **{c: 1 + i}),
+            deltas[i] or c if i < len(deltas) else c
+        )
+    return lambda s: ''.join(
+        mapAccumL(go)({})(s)[1]
+    )
+# ------------------------- TEST -------------------------
+def main():
+    '''Rule-set applied to a given string.'''
+    print(
+        nthInstanceReplaced({
+            'a': ['A', 'B', None, 'C', 'D'],
+            'b': ['E'],
+            'r': [None, 'F']
+        })(
+            "abracadabra"
+        )
+    )
+# ----------------------- GENERIC ------------------------
+# mapAccumL :: (acc -> x -> (acc, y)) ->
+# acc -> [x] -> (acc, [y])
+def mapAccumL(f):
+    '''A tuple of an accumulation and a map
+       with accumulation from left to right.
+    '''
+    def go(a, x):
+        return second(lambda v: a[1] + [v])(
+            f(a[0], x)
+        )
+    return lambda acc: lambda xs: reduce(
+        go, xs, (acc, [])
+    )
+# second :: (a -> b) -> ((c, a) -> (c, b))
+def second(f):
+    '''A simple function lifted to a function over a tuple,
+       with f applied only to the second of two values.
+    '''
+    return lambda xy: (xy[0], f(xy[1]))
+# MAIN ---
+if __name__ == '__main__':
+    main()</lang>
+{{Out}}
+<pre>AErBcadCbFD</pre>
 =={{header|Raku}}==