Prepend

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Prepend[expr,elem]

gives expr with elem prepended.

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Prepend[elem]

represents an operator form of Prepend that can be applied to an expression.

Details

Prepend works on SparseArray objects, returning ordinary lists if necessary.
Prepend can be used on Association objects. Single new elements are specified in the form key->value. New values replace older ones if their keys are the same.
Multiple elements to prepend to an association can be specified in the form {key₁->value₁,key₂->value₂, …}.
Prepend[elem][expr] is equivalent to Prepend[expr,elem].

Examples

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Basic Examples (3)Summary of the most common use cases

In[1]:=1

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https://wolfram.com/xid/0bn6byi-mm6

Out[1]=1

Prepend to an Association:

In[1]:=1

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https://wolfram.com/xid/0bn6byi-iovku2

Out[1]=1

Prepend several rules to an Association:

In[1]:=1

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https://wolfram.com/xid/0bn6byi-is8nxg

Out[1]=1

Generalizations & Extensions (1)Generalized and extended use cases

Use a head other than List:

In[1]:=1

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https://wolfram.com/xid/0bn6byi-caq

Out[1]=1

Applications (4)Sample problems that can be solved with this function

Prepend a row to a matrix:

In[1]:=1

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https://wolfram.com/xid/0bn6byi-ooq

Prepend to each row in a matrix:

In[1]:=1

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https://wolfram.com/xid/0bn6byi-wp9

Prepend a vector to a matrix:

In[1]:=1

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https://wolfram.com/xid/0bn6byi-sbm

Successively prepend to a list:

In[1]:=1

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https://wolfram.com/xid/0bn6byi-t2a

Out[1]=1

Possible Issues (1)Common pitfalls and unexpected behavior

In[1]:=1

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https://wolfram.com/xid/0bn6byi-luo

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0bn6byi-jbs

Out[2]=2

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