CODEWITHSUNDEEP
dataframeindexingiterationjulia
shaha
shaha

Reputation: 123

obtain index of a row in Julia dataframe (analogue of iterrows?)

Is there any way to obtain the index of a row and the row object while iterating through a df in Julia? If not, even a way to find the index of a row would be great, as I could simply use eachrow() and then find the iterated row's index, though I imagine this is less likely considering that naming a df's index isn't really supported in Julia.

For context, I need the index in order to find the first occurrence of 0 in each column of a df so that I can replace it with another value (say, 99). To do this, I want to iterate through all the rows of each column in a df. e.g. for df = DataFrame(a = [1, 0, 2], b = [0, 1, 0], c = [0, 0, 4]) the code:

for col_index in ["a", "b", "c"]
    for row in eachrow(select(df, :i))
        if row[1] == 0
            df[row.index, :i] = 99
            break
        end
    end
end

would turn df into

1 99 99
99 1 0 
2 0 4

Sorry if this is a silly question, though I could not find anything to the effect of either of my goals online.

Upvotes: 3

Views: 2966

Answers (2)

Bogumił Kamiński
Bogumił Kamiński

Reputation: 69949

  1. you can use rownumber function to get the row number in the data frame from which the DataFrameRow was taken.
  2. as DataFrameRow is mutable you can write your loop just as:
for col_index in ["a", "b", "c"]
    for row in eachrow(df)
        if row[col_index] == 0
            row[col_index] = 99
            break
        end
    end
end
  1. Finally it is faster to do what you want like this:
for col_index in ["a", "b", "c"]
    col = df[!, col_index]
    loc = findfirst(==(0), col)
    isnothing(loc) || (col[loc] = 99)
end

Upvotes: 1

shaha
shaha

Reputation: 123

You can get something which is good enough by using enumerate(eachrow(df)) h/t @Antonello.

From the toy code I wrote in the question, this looks like:

for col_index in ["a", "b", "c"]
    for (row_index, row) in enumerate(eachrow(select(df, :col_index)))
        if row[1] == 0
            df[row_index, :col_index] = 99
            break
        end
    end
end

Upvotes: 0

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