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I have this code to filter list of string that the first letter is capital:
fun f s = Char.isUpper(String.sub(s,0));
fun only_capitals (xs : string list) = List.filter(f , xs);
But when compile, I always receive error :
operator domain: 'Z -> bool
operand: (string -> bool) * string list
in expression:
List.filter (f,xs)
What does this error mean? How to fix it?
459
You can use the FILTER and COUNTIF functions to filter based on a list in Excel. To filter by a list in Excel, use the COUNTIF function to give an indication of whether or not each row meets your criteria, and then use the FILTER function to filter out the rows that do not meet your criteria.
filter(fn, list) Code language: Python (python) The filter() function iterates over the elements of the list and applies the fn() function to each element. It returns an iterator for the elements where the fn() returns True .
Short answer: To filter a list of lists for a condition on the inner lists, use the list comprehension statement [x for x in list if condition(x)] and replace condition(x) with your filtering condition that returns True to include inner list x , and False otherwise.
Type signature of List.filter is
val filter : ('a -> bool) -> 'a list -> 'a list
So you need to give List.filter two distinct arguments, not one argument which happens to be a tuple.
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