# In Sparse Matrices is posible condition in "combine"?

**URL:** <https://discourse.julialang.org/t/in-sparse-matrices-is-posible-condition-in-combine/6753>\
**Category:** General Usage\
**Created:** [October 29, 2017, 2:09pm UTC](https://discourse.julialang.org/t/in-sparse-matrices-is-posible-condition-in-combine/6753 "2017-10-29T14:09:05Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![programista](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/programista/32/5372_2.png) [@programista](https://discourse.julialang.org/u/programista)\
**Post date:** [October 29, 2017, 2:09pm UTC](https://discourse.julialang.org/t/in-sparse-matrices-is-posible-condition-in-combine/6753/1 "2017-10-29T14:09:05Z")

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sparse(I, J, V[, m, n, combine])

I must to igore new laue of V of old V is more then 0.

is posible condition in combine ?  
e.g: + if V=0 else skip…

Paul

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**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [October 29, 2017, 2:30pm UTC](https://discourse.julialang.org/t/in-sparse-matrices-is-posible-condition-in-combine/6753/2 "2017-10-29T14:30:54Z")

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> [@programista](#):
>
> igore new laue of V of old V is more then 0.

Please do make an effort to post something intelligible. If I decipher correctly, you may want something like

```julia
function sparse_new(I, J, V, W)
    _pick(w, v) = w > 0 ? w : v
    sparse(I, J, [_pick(W[i, j], v) for (i, j, v) in zip(I, J, V)])
end

```

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**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [October 29, 2017, 4:40pm UTC](https://discourse.julialang.org/t/in-sparse-matrices-is-posible-condition-in-combine/6753/3 "2017-10-29T16:40:56Z")

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> [@programista](#):
>
> sparse(I, J, V[, m, n, combine])

```julia
sparse(I, J, V, m, n, (a,b) -> a == 0 ? b : a)

```

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<div class="post-metadata">

**Author:** ![programista](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/programista/32/5372_2.png) [@programista](https://discourse.julialang.org/u/programista)\
**Post date:** [October 29, 2017, 5:02pm UTC](https://discourse.julialang.org/t/in-sparse-matrices-is-posible-condition-in-combine/6753/4 "2017-10-29T17:02:55Z")

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Thanks!

I undestend “a” is existing and “b” is new.

I need:

if b\<a → a-b  
if b==a → a

do it this rule : |  
sparse(I, J, V, m, n, (a,b) → b \< a ? a-b)|  
Paul;

W dniu 2017-10-29 o 17:46, kristoffer.carlsson pisze:

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**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [October 29, 2017, 7:13pm UTC](https://discourse.julialang.org/t/in-sparse-matrices-is-posible-condition-in-combine/6753/5 "2017-10-29T19:13:03Z")

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You havent said what to do when b \> a.