# Tensor subselectiom

**URL:** <https://itensor.discourse.group/t/tensor-subselectiom/879>\
**Category:** ITensor Julia Questions\
**Created:** [May 17, 2023, 4:28pm UTC](https://itensor.discourse.group/t/tensor-subselectiom/879 "2023-05-17T16:28:22Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![EmilioRui](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/emiliorui/32/208_2.png) [@EmilioRui](https://itensor.discourse.group/u/EmilioRui)\
**Post date:** [May 17, 2023, 4:28pm UTC](https://itensor.discourse.group/t/tensor-subselectiom/879/1 "2023-05-17T16:28:22Z")

</div>

Hi!  
Given an ITensor of N dimensions, how can I extract the first N-1 dimensions, at a fixed index for the last one?

I have a tensor:

```auto

ITensor ord=5 (dim=1|id=960|"Link,l=11") (dim=8|id=661|"Boson,Site,n=11") (dim=8|id=538|"Boson,Site,n=10") (dim=1|id=530|"Link,l=9") (dim=64|id=712|"Link,eigen")
NDTensors.Dense{Float64, Vector{Float64}}

```

and I would want:

```auto

ITensor ord=4 (dim=1|id=960|"Link,l=11") (dim=8|id=661|"Boson,Site,n=11") (dim=8|id=538|"Boson,Site,n=10") (dim=1|id=530|"Link,l=9") 
NDTensors.Dense{Float64, Vector{Float64}}

```

at a given index of Link,eigen index.

Thank you!

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<div class="post-metadata">

**Author:** ![ryanlevy](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/ryanlevy/32/150_2.png) [@ryanlevy](https://itensor.discourse.group/u/ryanlevy)\
**Post date:** [May 17, 2023, 6:10pm UTC](https://itensor.discourse.group/t/tensor-subselectiom/879/2 "2023-05-17T18:10:52Z")

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Would something like this work?

```julia
julia> i, j, k, l = Index.((2, 3, 4, 5))
((dim=2|id=906), (dim=3|id=19), (dim=4|id=39), (dim=5|id=733))

julia> A = randomITensor(i, j, k, l)
ITensor ord=4 (dim=2|id=906) (dim=3|id=19) (dim=4|id=39) (dim=5|id=733)
NDTensors.Dense{Float64, Vector{Float64}}

julia> B = A * onehot(l=>1)
ITensor ord=3 (dim=2|id=906) (dim=3|id=19) (dim=4|id=39)
NDTensors.Dense{Float64, Vector{Float64}}

```

([onehot docs](https://itensor.github.io/ITensors.jl/stable/ITensorType.html#ITensors.onehot))

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<div class="post-metadata">

**Author:** ![EmilioRui](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/emiliorui/32/208_2.png) [@EmilioRui](https://itensor.discourse.group/u/EmilioRui)\
**Post date:** [May 19, 2023, 9:26am UTC](https://itensor.discourse.group/t/tensor-subselectiom/879/3 "2023-05-19T09:26:36Z")

</div>

It works, thank you so much!