# Using nonunique() with multiple dataframe columns

**URL:** <https://discourse.julialang.org/t/using-nonunique-with-multiple-dataframe-columns/64523>\
**Category:** General Usage\
**Tags:** question, dataframes\
**Created:** [July 12, 2021, 5:49pm UTC](https://discourse.julialang.org/t/using-nonunique-with-multiple-dataframe-columns/64523 "2021-07-12T17:49:59Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![kbot](https://avatars.discourse-cdn.com/v4/letter/k/e9c0ed/32.png) [@kbot](https://discourse.julialang.org/u/kbot)\
**Post date:** [July 12, 2021, 5:49pm UTC](https://discourse.julialang.org/t/using-nonunique-with-multiple-dataframe-columns/64523/1 "2021-07-12T17:49:59Z")

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Hi,

I’d like to identify rows with duplicate values across multiple columns (i.e. colA && colC && colD) with something like

findall( nonunique( df, CONDITION) )

for one column CONDITION is easy e.g. :colA.

How can I do this for multiple, non-contiguous columns?

Thanks for any help,

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<div class="post-metadata">

**Author:** ![pdeffebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pdeffebach/32/10320_2.png) [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)\
**Post date:** [July 12, 2021, 5:53pm UTC](https://discourse.julialang.org/t/using-nonunique-with-multiple-dataframe-columns/64523/2 "2021-07-12T17:53:05Z")

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Give a vector of column names

```julia
julia> df = DataFrame(a = [1, 2, 1], b = [4, 5, 4])
3×2 DataFrame
 Row │ a b
     │ Int64 Int64
─────┼──────────────
   1 │ 1 4
   2 │ 2 5
   3 │ 1 4

julia> nonunique(df, :a)
3-element Vector{Bool}:
 0
 0
 1

julia> nonunique(df, [:a, :b])
3-element Vector{Bool}:
 0
 0
 1

```

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<div class="post-metadata">

**Author:** ![kbot](https://avatars.discourse-cdn.com/v4/letter/k/e9c0ed/32.png) [@kbot](https://discourse.julialang.org/u/kbot)\
**Post date:** [July 13, 2021, 7:54am UTC](https://discourse.julialang.org/t/using-nonunique-with-multiple-dataframe-columns/64523/3 "2021-07-13T07:54:14Z")

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Thanks, simple!