# How to select dataframe column by name?
**URL:** https://discourse.julialang.org/t/how-to-select-dataframe-column-by-name/67048
**Category:** New to Julia
**Tags:** dataframes
**Created:** [August 26, 2021, 4:33pm UTC](https://discourse.julialang.org/t/how-to-select-dataframe-column-by-name/67048 "2021-08-26T16:33:13Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)
#### Post date: [August 26, 2021, 4:33pm UTC](https://discourse.julialang.org/t/how-to-select-dataframe-column-by-name/67048/1 "2021-08-26T16:33:13Z")
Hello,
I have a dataframe and I am selecting row based on a condition. How can I select a column based on its name?
Here I can get column X but the result is a string instead of a numeric vector. If I use the names of the column not enclosed in brackets it does not work, as expected because the object X is not defined.
What is the correct way?
Thank you
```julia
julia> df[df.Bact .== "A. vinelandii", :]
18×3 DataFrame
Row │ Bact X Y
│ String String String
─────┼────────────────────────────────────────────────────
1 │ A. vinelandii 0.050561797752809 1314042485.29793
2 │ A. vinelandii 0.252808988764045 1224431687.48933
3 │ A. vinelandii 0.502808988764045 1038388615.87881
4 │ A. vinelandii 0.932584269662921 657651643.874837
5 │ A. vinelandii 1.19662921348315 403011067.968018
6 │ A. vinelandii 1.89606741573034 147820324.502811
7 │ A. vinelandii 2.21629213483146 100946201.037493
8 │ A. vinelandii 2.82865168539326 80524951.2089802
9 │ A. vinelandii 0.039325842696629 79770165.0793892
10 │ A. vinelandii 0.235955056179775 99530230.5872667
11 │ A. vinelandii 0.5 232302118.140757
12 │ A. vinelandii 0.943820224719101 615695604.542686
13 │ A. vinelandii 1.19662921348315 949522176.82357
14 │ A. vinelandii 1.37921348314607 1236017272.81974
15 │ A. vinelandii 1.69101123595506 1450621774.81555
16 │ A. vinelandii 1.88202247191011 1471259098.32493
17 │ A. vinelandii 2.1938202247191 1370926953.01064
18 │ A. vinelandii 2.79213483146067 1464347573.09895
julia> df[df.Bact .== "A. vinelandii", "X"]
18-element Vector{String}:
"0.050561797752809"
"0.252808988764045"
"0.502808988764045"
"0.932584269662921"
"1.19662921348315"
"1.89606741573034"
"2.21629213483146"
"2.82865168539326"
"0.039325842696629"
"0.235955056179775"
"0.5"
"0.943820224719101"
"1.19662921348315"
"1.37921348314607"
"1.69101123595506"
"1.88202247191011"
"2.1938202247191"
"2.79213483146067"
julia> df[df.Bact .== "A. vinelandii", X]
ERROR: UndefVarError: X not defined
Stacktrace:
[1] top-level scope
@ none:1
```
PS: I see that the dataframe is already an all-string one, so it is the way I used the correct method? Then I have to reconvert the array to numeric. Is there a way to tell Julia to read numbers from a spreadsheet directly?
---
### Author:  [@awasserman](https://discourse.julialang.org/u/awasserman)
#### Post date: [August 26, 2021, 5:09pm UTC](https://discourse.julialang.org/t/how-to-select-dataframe-column-by-name/67048/2 "2021-08-26T17:09:21Z")
How are you creating this dataframe? If you’re loading it from a csv file using [`CSV.jl`](https://github.com/JuliaData/CSV.jl) then it should automatically detect any columns of numerical data and parse them as the correct type.
---
### Author:  [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)
#### Post date: [August 26, 2021, 5:16pm UTC](https://discourse.julialang.org/t/how-to-select-dataframe-column-by-name/67048/3 "2021-08-26T17:16:57Z")
I am loading with:
```julia
using DataFrames, CSV
df = CSV.read("Data.tsv", DataFrame;
delim='\t', missingstring="NA", decimal=',', copycols=true)
```
---
### Author:  [@awasserman](https://discourse.julialang.org/u/awasserman)
#### Post date: [August 26, 2021, 5:46pm UTC](https://discourse.julialang.org/t/how-to-select-dataframe-column-by-name/67048/4 "2021-08-26T17:46:55Z")
It’s possible that the fields `X` and `Y` have entries that aren’t parsed as numerical data in the source tsv file. If you try to force CSV to parse a column as a float, it should identify any bad rows in a warning message.
```julia
df = CSV.read(
"Data.tsv", DataFrame;
delim='\t',
missingstring="NA",
decimal=',',
types=Dict(:X => Float64, :Y => Float64)
)
```
---
### Author:  [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)
#### Post date: [August 26, 2021, 7:55pm UTC](https://discourse.julialang.org/t/how-to-select-dataframe-column-by-name/67048/5 "2021-08-26T19:55:04Z")
Select a column with `df[:, :col]` or `df[:, "col"]`.
---
### Author:  [@piever](https://discourse.julialang.org/u/piever)
#### Post date: [August 26, 2021, 10:00pm UTC](https://discourse.julialang.org/t/how-to-select-dataframe-column-by-name/67048/6 "2021-08-26T22:00:01Z")
Looks like the CSV file is using `.` as a decimal separator, so probably passing `decimal = ','` to `CSV.read` causes the parsing of floating point numbers to fail. Did you try passing `decimal = '.'` or omitting that setting altogether?
---
### Author:  [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)
#### Post date: [August 27, 2021, 7:05am UTC](https://discourse.julialang.org/t/how-to-select-dataframe-column-by-name/67048/7 "2021-08-27T07:05:20Z")
Ops, the `,` was a typo. Thanks!