How to replace/set/change value in array/dataframe if value is less/greater than?

New to Julia
1

Hello, I had some code that used to work but it must have been for a previous version of Julia. I can’t find what I am looking for in the DataFrame docs Getting Started · DataFrames.jl

I want to replace values in an array or DataFrame that are less than 0.5 to 0.0.

QWER = rand(5, 5)
QWER[QWER .>= 0.5] .= 0.0

This gives a 12 element view, everything is set to 0.0.

QWER = [QWER .<= 0.5] .= 0.0

This gives the error
MethodError: Cannotconvert an object of type Float64 to an object of type BitArray{2}

using DataFrames
QWER = DataFrame(QWER)
QWER = [QWER .<= 0.5] .= 0.0

This gives the error
MethodError: Cannot convert an object of type Float64 to an object of type BitArray{2}

QWER[QWER .>= 0.5] .= 0.0

This gives the error
MethodError: no method matching getindex(::DataFrame, ::DataFrame)

What is the correct way to do this?
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Answer edit:

For a DataFrame

2

For Arrays the first solution is correct. Just look at QWER.
For DataFrames something like

df[df.col1 .> 0.5,:col1] .= 0.0

should do the trick

1 Like
3

Thank you for your reply - you are correct, the arrays solution works.

Does the DataFrames on not just specify the first column (assuming it is named col1)?

4

Yes, if you want to change all of the columns, then use

QWER .= ifelse.(QWER .> 0.5, 0.0, QWER)
4 Likes