On Friday, September 4, 2015 at 7:55:30 AM UTC-6, Helder wrote:
> Hi,
> I've got the next problem, using a lambda function in the python sorted function.
>
> Consider this easy python example:
>
> d0 = {'sorted': 1, 'unsorted': 0}
> d1 = {'sorted': 5, 'unsorted': 1}
> d2 = {'sorted': 3, 'unsorted': 2}
> d3 = {'sorted': 7, 'unsorted': 3}
> d4 = {'sorted': 4, 'unsorted': 4}
> l = [d0,d1,d2,d3,d4]
> sorted(l, key = lambda x:x['sorted'])
>
> The result would be:
> [{'sorted': 1, 'unsorted': 0},
> {'sorted': 3, 'unsorted': 2},
> {'sorted': 4, 'unsorted': 4},
> {'sorted': 5, 'unsorted': 1},
> {'sorted': 7, 'unsorted': 3}]
>
> Now if I would want to do this in IDL, things would get difficult. Suppose I get a dictionary (or a simple object with a property...) as a result of an operation and I want to sort this result according to a specific property... how do I do that in IDL?
>
> The synthax:
> matches = Python.sorted(matches, key = lambda(x: x.distance))
>
> will give me a compilation error.
>
> Thanks,
> Helder
>
> PS: I found a different solution to this problem using IDL. I import all properties in an idl variable, sort the variable and apply this to the list. A python solution would be though nice, just to know how to deal with lambda functions.
Hi Helder,
Unfortunately, IDL can't translate its Lambda functions into Python lambda functions. If you wanted to have Python do this, you could transfer the variable over to Python, and then execute a Python command. Like this:
IDL> d0 = hash('sorted', 1, 'unsorted', -1)
IDL> d1 = hash('sorted', 5, 'unsorted', 1)
IDL> d2 = hash('sorted', 3, 'unsorted', 2)
IDL> d3 = hash('sorted', 7, 'unsorted', 3)
IDL> d4 = hash('sorted', 4, 'unsorted', 4)
IDL> lst = list(d0,d1,d2,d3,d4)
IDL> Python.l = lst
IDL> >>>result = sorted(l, key = lambda x:x['sorted'])
IDL> result = Python.result
IDL> print, result, /implied
Now, if you wanted to do this purely in IDL, you could use List::Sort with a Lambda compare function, and the new .Compare method, which exists on IDL variables:
d0 = {sorted: 1, unsorted: 0}
d1 = {sorted: 5, unsorted: 1}
d2 = {sorted: 3, unsorted: 2}
d3 = {sorted: 7, unsorted: 3}
d4 = {sorted: 4, unsorted: 4}
lst = List(d0,d1,d2,d3,d4)
result = lst.Sort(COMPARE=Lambda(a,b:(a.sorted).Compare(b.sorted)))
print, result, /implied
Here's an example of how the .Compare method works:
IDL> print, (1).compare(2)
-1
IDL> print, (1).compare(1)
0
IDL> print, (1).compare(0)
1
Cheers,
Chris
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