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I have some equations that I would like to group according to specified terms.

For example, $x_1x_2x_3+x_1x_2x_4+x_1x_5x_6+3x_1x_2x_3$.

I would like this to be grouped as $3x_1x_2x_3+x_1x_2x_4+x_1x_5x_6$.

However, when using Collect in Mathematica, it is grouping them as $x_1(3x_2x_3+x_2x_4+x_5x_6)$.

I am currently specifying all possible combinations $x_i, x_ix_j$ and $x_ix_jx_k$ as the terms I would like to group by. Selecting just the third order terms isn't an option here for what I need to use it for.

Is there anyway to stop it factorising the expressions?

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  • $\begingroup$ It is not clear, what do you want to achieve. In particular, the term 3x1x2x3+x1x2x4+x1x5x6 is only a part of the starting expression, and the words "I would like this to be grouped as..." are unclear. I suggest that you take a minimal expression and show both its initial and its final forms. It would be also a good idea if you explain the reason for this operation. For example, if it is an intermediate calculation step, it is one thing. If it is a final representation of your result - the other. Besides, please write all the expressions in Mathematical notations in acopy-paste ready form. $\endgroup$ May 6, 2021 at 12:24
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    $\begingroup$ The out put of your expression in MMA version 12.1 is : 4 x1 x2 x3 + x1 x2 x4 + x1 x5 x6 $\endgroup$ May 6, 2021 at 12:53

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