Retrieving Dictionary Value Best Practices

Question

I just recently noticed Dictionary TryGetValue TKey key  out TValue value  and was curious as to which is the better approach to retrieving a value from the Dictionary   I ve traditionally done   if  myDict Contains someKey        someVal   myDict someKey              unless I know it has to be in there   Is it better to just do   if  myDict TryGetValue somekey  out someVal            Which is the better practice  Is one faster than the other  I would imagine that the Try version would be slower as its  swallowing  a try catch inside itself and using that as logic  no

User · Answer

Well in fact TryGetValue is faster  How much faster  It depends on the dataset at hand  When you call the Contains method  Dictionary does an internal search to find its index  If it returns true  you need another index search to get the actual value  When you use TryGetValue  it searches only once for the index and if found  it assigns the value to your variable   Edit   Ok  I understand your confusion so let me elaborate   Case 1   if  myDict Contains someKey        someVal   myDict someKey     In this case there are 2 calls to FindEntry  one to check if the key exists and one to retrieve it  Case 2   myDict TryGetValue somekey  out someVal    In this case there is only one call to FindKey because the resulting index is kept for the actual retrieval in the same method

User · Answer

Well in fact TryGetValue is faster  How much faster  It depends on the dataset at hand  When you call the Contains method  Dictionary does an internal search to find its index  If it returns true  you need another index search to get the actual value  When you use TryGetValue  it searches only once for the index and if found  it assigns the value to your variable   Edit   Ok  I understand your confusion so let me elaborate   Case 1   if  myDict Contains someKey        someVal   myDict someKey     In this case there are 2 calls to FindEntry  one to check if the key exists and one to retrieve it  Case 2   myDict TryGetValue somekey  out someVal    In this case there is only one call to FindKey because the resulting index is kept for the actual retrieval in the same method

User · Answer

TryGetValue is slightly faster  because FindEntry will only be called once       How much faster  It depends on the   dataset at hand  When you call the   Contains method  Dictionary does an   internal search to find its index  If   it returns true  you need another   index search to get the actual value    When you use TryGetValue  it searches   only once for the index and if found    it assigns the value to your variable    FYI  It s not actually catching an error    It s calling   public bool TryGetValue TKey key  out TValue value        int index   this FindEntry key       if  index  gt   0                value   this entries index  value          return true            value   default TValue       return false      ContainsKey is this   public bool ContainsKey TKey key        return  this FindEntry key   gt   0

User · Answer

Well in fact TryGetValue is faster  How much faster  It depends on the dataset at hand  When you call the Contains method  Dictionary does an internal search to find its index  If it returns true  you need another index search to get the actual value  When you use TryGetValue  it searches only once for the index and if found  it assigns the value to your variable   Edit   Ok  I understand your confusion so let me elaborate   Case 1   if  myDict Contains someKey        someVal   myDict someKey     In this case there are 2 calls to FindEntry  one to check if the key exists and one to retrieve it  Case 2   myDict TryGetValue somekey  out someVal    In this case there is only one call to FindKey because the resulting index is kept for the actual retrieval in the same method

User · Answer

TryGetValue is slightly faster  because FindEntry will only be called once       How much faster  It depends on the   dataset at hand  When you call the   Contains method  Dictionary does an   internal search to find its index  If   it returns true  you need another   index search to get the actual value    When you use TryGetValue  it searches   only once for the index and if found    it assigns the value to your variable    FYI  It s not actually catching an error    It s calling   public bool TryGetValue TKey key  out TValue value        int index   this FindEntry key       if  index  gt   0                value   this entries index  value          return true            value   default TValue       return false      ContainsKey is this   public bool ContainsKey TKey key        return  this FindEntry key   gt   0

User · Answer

I imagine that trygetvalue is doing something more like   if myDict ReallyOptimisedVersionofContains someKey        someVal   myDict someKey     return true    return false    So hopefully no try catch anywhere   I think it is just a method of convenience really  I generally use it as it saves a line of code or two

User · Answer

Well in fact TryGetValue is faster  How much faster  It depends on the dataset at hand  When you call the Contains method  Dictionary does an internal search to find its index  If it returns true  you need another index search to get the actual value  When you use TryGetValue  it searches only once for the index and if found  it assigns the value to your variable   Edit   Ok  I understand your confusion so let me elaborate   Case 1   if  myDict Contains someKey        someVal   myDict someKey     In this case there are 2 calls to FindEntry  one to check if the key exists and one to retrieve it  Case 2   myDict TryGetValue somekey  out someVal    In this case there is only one call to FindKey because the resulting index is kept for the actual retrieval in the same method

User · Answer

I imagine that trygetvalue is doing something more like   if myDict ReallyOptimisedVersionofContains someKey        someVal   myDict someKey     return true    return false    So hopefully no try catch anywhere   I think it is just a method of convenience really  I generally use it as it saves a line of code or two

User · Answer

TryGetValue is slightly faster  because FindEntry will only be called once       How much faster  It depends on the   dataset at hand  When you call the   Contains method  Dictionary does an   internal search to find its index  If   it returns true  you need another   index search to get the actual value    When you use TryGetValue  it searches   only once for the index and if found    it assigns the value to your variable    FYI  It s not actually catching an error    It s calling   public bool TryGetValue TKey key  out TValue value        int index   this FindEntry key       if  index  gt   0                value   this entries index  value          return true            value   default TValue       return false      ContainsKey is this   public bool ContainsKey TKey key        return  this FindEntry key   gt   0

User · Answer

I imagine that trygetvalue is doing something more like   if myDict ReallyOptimisedVersionofContains someKey        someVal   myDict someKey     return true    return false    So hopefully no try catch anywhere   I think it is just a method of convenience really  I generally use it as it saves a line of code or two

User · Answer

I imagine that trygetvalue is doing something more like   if myDict ReallyOptimisedVersionofContains someKey        someVal   myDict someKey     return true    return false    So hopefully no try catch anywhere   I think it is just a method of convenience really  I generally use it as it saves a line of code or two

User · Answer

TryGetValue is slightly faster  because FindEntry will only be called once       How much faster  It depends on the   dataset at hand  When you call the   Contains method  Dictionary does an   internal search to find its index  If   it returns true  you need another   index search to get the actual value    When you use TryGetValue  it searches   only once for the index and if found    it assigns the value to your variable    FYI  It s not actually catching an error    It s calling   public bool TryGetValue TKey key  out TValue value        int index   this FindEntry key       if  index  gt   0                value   this entries index  value          return true            value   default TValue       return false      ContainsKey is this   public bool ContainsKey TKey key        return  this FindEntry key   gt   0

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