CODEWITHSUNDEEP
f#deedle
İrem Erten
İrem Erten

Reputation: 137

Filtering Rows in F#

I have a code where I have the following frame and filter rows as follows:

let dfff= 
[ "year" => series [ 1 => 1990.0; 2 => 1991.00; 3 => 1992.0;  4 => 1993.0]
  "gold"  => series [ 1 => 10.0; 2 => 10.00; 3 => 15.0; 4 => 20.0] 
  "silver"  => series [ 1 => 20.0; 2 => 30.00; 3 => 45.0; 4 => 55.0] ] 
|> frame

let dfff2 = dfff |> Frame.filterRows (fun key row  -> row?year <= 1992.0 )

Why do I have to write key in 

Frame.filterRows (fun key row  -> row?year <= 1992.0)

if my function only depends on row? What role does key play here? I will appreciate if anybody could explain me the logic. Thanks!

Upvotes: 1

Views: 453

Answers (1)

Tomas Petricek
Tomas Petricek

Reputation: 243106

In Deedle, frames have row keys and column keys. In your case, you have Frame<int, string> meaning that the row keys are integers (just numbers) and column keys are strings (column names) - but you might also have dates or other more interesting things as row keys.

The filterRows function gives you the row key together with row data. The key parameter is just the row key - in your case, this is (uninteresting) int index, but it might be e.g. useful date in other scenarios.

F# lets you write _ to explicitly ignore the value:

let dfff2 = dfff |> Frame.filterRows (fun _ row  -> row?year <= 1992.0 )

In the Series module, we have Series.filter and Series.filterValues where the first one gives you key & value and the second one gives you just the value. So, we could follow the same pattern and add Frame.filterRowValues.

This would actually be quite easy, so if you want to contribute, please send a pull request with a change somewhere around here :-).

Upvotes: 3

Related Questions