Android Question Use a char as the key for a map

Alessandro71 · Apr 3, 2020

Something I wasn't able to find: how to declare a char in the IDE that is not CHR(xx)
"A" is really string, not a single char, and I need a map as the following:

B4X:

Dim countrymap As Map = CreateMap( _
    "1": "USA", _
    "3": "Mexico", _
    "5": "USA", _
    "J": "Japan", _
    "S": "UK" _
)

How can I specify the key as a single char?

Jeffrey Cameron · Apr 3, 2020

Technically, "1" is also a char as well as a string so I'm not sure what you are trying to accomplish. But, to answer your question:

B4X:

Dim countrymap As Map = CreateMap( _
         Chr(Asc("1")): "USA", _
        Chr(Asc("3")): "Mexico", _
        Chr(Asc("5")): "USA", _
        Chr(Asc("J")): "Japan", _
        Chr(Asc("S")): "UK" _
        )

For context:

B4X:

    Dim pcChar As Char = Asc("A")
    Dim psString As String = "A"
    
    If pcChar = psString Then
        Log("Char = String")
    Else
        Log("Char <> String")
    End If
    If pcChar = "A" Then
        Log("Char = 'A'")
    Else
        Log("Char <> 'A'")
    End If
    If pcChar = 65 Then
        Log("Char = 65")
    Else
        Log("Char <> 65")
    End If

Log output:

B4X:

** Activity (main) Create, isFirst = true **
Char <> String
Char <> 'A'
Char = 65

Alessandro71 · Apr 4, 2020

thank you for your answer
to add a little more context

B4X:

countrymap.Get(m_VIN.CharAt(0))

won't work with my first declaration, while it works with yours
i was wondering if there's a more compact way to specify a single char instead of chr(asc(x))

stevel05 · Apr 4, 2020

What you don't say is why you want to use a Char as a key for the map.
EDIT: sorry you did.

If you are getting the keys from somewhere else to query the map, it may be easier to use strings and convert the key to a string on accessing the map, something like:

B4X:

M.Get(Key & "")

stevel05 · Apr 4, 2020

Where is m_VIN defined? You could use a string array, or list or even substring instead of extracting a char

Alessandro71 · Apr 4, 2020

stevel05 said:
If you are getting the keys from somewhere else to query the map, it may be easier to use strings and convert the key to a string on accessing the map, something like:

B4X:

M.Get(Key & "")

thanks for your clever way to convert a char to a string on the fly: i missed it
but i still prefer to avoid conversions and work only with the minimal data required

Alessandro71 · Apr 4, 2020

stevel05 said:
Where is m_VIN defined? You could use a string array, or list or even substring instead of extracting a char

it's just a string defined elsewhere
i think extracting a single char is faster than a substr

stevel05 · Apr 4, 2020

Alessandro71 said:
i think extracting a single char is faster than a substr

Is speed an issue over simplicity.

If you are accessing the map key via an index, do you really need to use a map at all? you could access a list directly via the index.

Alessandro71 · Apr 4, 2020

stevel05 said:
If you are accessing the map key via an index, do you really need to use a map at all? you could access a list directly via the index.

code maintainability: a map declared in the global sections has better readability than a runtime built list

Erel · Apr 5, 2020

Alessandro71 said:
i think extracting a single char is faster than a substr

This is a big mistake.

1. Your assumption is wrong.
2. Unless you are creating a map with 100M+ items such optimizations will never make any effect.

Watch the performance video tutorial: https://www.b4x.com/etp.html

Alessandro71 · Apr 5, 2020

always enlightening
thank you

Android Question Use a char as the key for a map

Alessandro71

Well-Known Member

Jeffrey Cameron

Well-Known Member

Alessandro71

Well-Known Member

stevel05

Expert

stevel05

Expert

Alessandro71

Well-Known Member

Alessandro71

Well-Known Member

stevel05

Expert

Alessandro71

Well-Known Member

Erel

B4X founder

Alessandro71

Well-Known Member

Similar Threads

Android Question Use a char as the key for a map

Well-Known Member

Well-Known Member

Well-Known Member

Expert

Expert

Well-Known Member

Well-Known Member

Expert

Well-Known Member

B4X founder

Well-Known Member

Similar Threads

Privacy & Transparency

Privacy & Transparency