Execute comparison (calculate distance) between columns in two DataFrames using GeoPandas if values in their rows are equal?

Question

I have df1 and df2. Each dataframe contains an ID column. Each dataframe also contains a geometry column. I would like to calculate the distance between each dataframe's geometry column only for rows where ID's match in each dataframe.

I would imagine it looks something like this but can't figure it out:

for geom in df1.geometry:
    if df1['system_id'] == df2f['systemID']:    
        df1['distance'] = [geom.distance(df2.geometry[0].boundary) for geom in df1.geometry]

Answer 1

Merge the two dataframes into a temporary dataframe, calculate the distances and merge the result back to the original data frame:

#Merge the two dataframes where ids match into a new dataframe
distances = df1.merge(right=df2, how="inner",left_on="system_id", right_on="systemID")

#Calculate distances
distances["distance"] = distances.apply(lambda row: row["geometry_x"].distance(row["geometry_y"].boundary), axis=1)

#Merge distance column to the original dataframe. Distance will be NaN for rows with no id match
df1 = df1.merge(right=distances[["system_id","distance"]], how="left", on="system_id")