Basic Examples (4) 

Create a Tabular expression:

In[1]:=

Out[1]=

Create an association between two columns of the Tabular:

In[2]:=

Out[2]=

Create a nested association with three columns:

In[3]:=

Out[3]=

If the first column contains duplicate keys, you can choose to merge them through a function specified as third argument:

In[4]:=

Out[4]=

Scope (4) 

Use an alternative syntax with a Rule for each level of nesting:

In[5]:=

Out[5]=

In[6]:=

Out[6]=

Create an association with multiple columns as Values:

In[7]:=

Out[7]=

In[8]:=

Out[8]=

Use multiple columns as Keys:

In[9]:=

Out[9]=

In[10]:=

Out[10]=

In[11]:=

Out[11]=

Create an arbitrarily nested association and visualize it as a Dataset:

In[12]:=

In[13]:=

Out[13]=

In[14]:=

Out[14]=

Specify a different merging function for each level of nesting:

In[15]:=

Out[15]=

Options (2) 

DuplicatesWarning (2) 

Return a warning message when the column of the Keys contains duplicates and no merging function is specified:

In[16]:=

Out[16]=

In[17]:=

Out[17]=

---

To avoid this message, you can just specify a merging function as the third argument, or set the option "DuplicatesWarning" to False, to obtain the automatic merging through Identity without error messages:

In[18]:=

Out[18]=

In[19]:=

Out[19]=

In[20]:=

Out[20]=

Applications (2) 

Create an association between the coordinates and magnitudes of earthquakes:

In[21]:=

Out[21]=

In[22]:=

Out[22]=

Use it to create a GeoHistogram of US seismicity:

In[23]:=

Out[23]=

Properties and Relations (2) 

In the simplest case with only 2 columns, if there are no duplicates in the column of the keys, AssociateColumn[tab,{col1,col2}] is equivalent to Association[Rule@@@Values@Normal@tab[[All,{col1,col2}]]]:

In[24]:=

Out[24]=

In[25]:=

Out[25]=

In[26]:=

Out[26]=

In[27]:=

Out[27]=

If there are duplicates in the column of the keys, AssociateColumns[tab, {col1,col2},f] is equivalent to Map[f,GroupBy[Values@Normal@tab[[All,{col1,col2}]],First→Last]]:

In[28]:=

Out[28]=

In[29]:=

Out[29]=

In[30]:=

Out[30]=

Possible Issues (2) 

The merging functions should be actually allowed by the structure of the data:

In[31]:=

In[32]:=

Out[32]=

In[33]:=

Out[33]=

In[34]:=

Out[34]=

Sometimes the error messages suggest what to change:

In[35]:=

Out[35]=

In[36]:=

Out[36]=

In[37]:=

Out[37]=