# Mutate a new variable with row numbers
**URL:** https://discourse.julialang.org/t/mutate-a-new-variable-with-row-numbers/30985
**Category:** Data
**Created:** [November 12, 2019, 1:52am UTC](https://discourse.julialang.org/t/mutate-a-new-variable-with-row-numbers/30985 "2019-11-12T01:52:56Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@pradeip1](https://discourse.julialang.org/u/pradeip1)
#### Post date: [November 12, 2019, 1:52am UTC](https://discourse.julialang.org/t/mutate-a-new-variable-with-row-numbers/30985/1 "2019-11-12T01:52:56Z")
how to add a row number using Queryverse in Julia?
for example in R I simply use ID = row\_number()
---
### Author:  [@longemen3000](https://discourse.julialang.org/u/longemen3000)
#### Post date: [November 12, 2019, 5:37am UTC](https://discourse.julialang.org/t/mutate-a-new-variable-with-row-numbers/30985/2 "2019-11-12T05:37:27Z")
Hi, welcome to the Julia Discourse!
i dont know if there is a function dedicated for this, but you can do:
```julia
df = DataFrame(a=[1, 2, 3], b=[:a, :b, :c]) #example dataframe
3×2 DataFrame
│ Row │ a │ b │
│ │ Int64 │ Symbol │
├─────┼───────┼────────┤
│ 1 │ 1 │ a │
│ 2 │ 2 │ b │
│ 3 │ 3 │ c │
df[!,:row_number] = 1:size(df,1) #the ! means an unsafe modification of df
julia> df
3×3 DataFrame
│ Row │ a │ b │ row_number │
│ │ Int64 │ Symbol │ Int64 │
├─────┼───────┼────────┼────────────┤
│ 1 │ 1 │ a │ 1 │
│ 2 │ 2 │ b │ 2 │
│ 3 │ 3 │ c │ 3 │
```
for more information about indexing, you can check [here](http://juliadata.github.io/DataFrames.jl/stable/lib/indexing/)
edit: changed to `size(df,1)`, my bad
---
### Author:  [@pradeip1](https://discourse.julialang.org/u/pradeip1)
#### Post date: [November 12, 2019, 9:13am UTC](https://discourse.julialang.org/t/mutate-a-new-variable-with-row-numbers/30985/3 "2019-11-12T09:13:25Z")
Thanks…but this only works when I have the following:
**df[!,:row\_number] = 1:size(df, 1)**
otherwise, I get this error:
---
### Author:  [@nilshg](https://discourse.julialang.org/u/nilshg)
#### Post date: [November 12, 2019, 10:16am UTC](https://discourse.julialang.org/t/mutate-a-new-variable-with-row-numbers/30985/4 "2019-11-12T10:16:51Z")
I think @longemen3000 meant to write `size(df, 1)` above - which returns the number of rows of a DataFrame (in his example there are as many rows as columns so it didn’t matter!)
Consider:
```julia
julia> using DataFrames
julia> df = DataFrame(a = rand(5), b = rand(5))
5×2 DataFrame
│ Row │ a │ b │
│ │ Float64 │ Float64 │
├─────┼──────────┼──────────┤
│ 1 │ 0.814602 │ 0.826607 │
│ 2 │ 0.361759 │ 0.631964 │
│ 3 │ 0.937936 │ 0.485979 │
│ 4 │ 0.755144 │ 0.526638 │
│ 5 │ 0.932572 │ 0.577122 │
julia> size(df, 1)
5
julia> size(df, 2)
3
```
You could instead use the `nrow` function which might be safer than remembering which dimension to call `size` on:
```julia
julia> df[!, :row_number] = 1:nrow(df)
1:5
julia> df
5×3 DataFrame
│ Row │ a │ b │ row_number │
│ │ Float64 │ Float64 │ Int64 │
├─────┼──────────┼──────────┼────────────┤
│ 1 │ 0.814602 │ 0.826607 │ 1 │
│ 2 │ 0.361759 │ 0.631964 │ 2 │
│ 3 │ 0.937936 │ 0.485979 │ 3 │
│ 4 │ 0.755144 │ 0.526638 │ 4 │
│ 5 │ 0.932572 │ 0.577122 │ 5 │
```
---
### Author:  [@Mattriks](https://discourse.julialang.org/u/Mattriks)
#### Post date: [November 12, 2019, 10:41am UTC](https://discourse.julialang.org/t/mutate-a-new-variable-with-row-numbers/30985/5 "2019-11-12T10:41:48Z")
or:
```julia
df.row = axes(df, 1)
```
For more info: `?axes`