How to add an extra column to a current matrix (list)? [duplicate]

Question

a = {{-800, 1712}, {-801, 1713}, {-806, 1832}} TableForm[a] b = a[[All, 2]] - Min[a[[All, 2]]]

How do I make a new matrix (list) whic looks like this

-800 1712 0 -801 1713 1 -806 1832 120

The 3rd column, takes the difference between the value from the 2nd column and it's minimum of the whole 2nd column.

I tried to Join the two, but with no success.

Thanks.

Jagra · Accepted Answer · 2015-04-15 23:40:18Z

Perhaps I've missed something, but you seem to just want to append a vector (which you have already calculated) to a matrix.

Documentation for Append[] shows how to do it:

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For your case since you already have a and b:

MapThread[Append, {a, b}] // MatrixForm

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A different approach enables you to join matrixes to make longer rows:

The following makes a 2 column matrix from your b

b2 = Transpose[{b, b}]; b2 // MatrixForm

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The documentation for Join[] shows the way to do what you asked for in your comment:

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Note that the 2 at the end of the Join[] operates as a level specification.

For your case:

Join[a, b2, 2]; % // MatrixForm

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How would I Append two columns? Do I have to use MapThread[Append, { MapThread[Append, {a, b}], b} ] // TableForm, or there is an easy way? Thanks. — Chen Stats Yu
– Chen Stats Yu, Commented Dec 6, 2014 at 16:34

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