Expression iterator

[xdssio]

I found myself needing to zip columns all the time.
This makes expressions look and feel a bit more like a list.

1. Implement __len__

len(df.x) == len(df)

2. Implement __iterator__

• I used chunks of 1000

Example

# this holds 1000 values in memory at a time
for x in df.x:
  <x> as values

# This bring all values into memory
for x in df.x.values.tolist(): 
   pass

This makes zip works efficiently :

for x,y in zip(df.x,df.y):
   pass
 

[maartenbreddels]

This makes zip works efficiently :

for x,y in zip(df.x,df.y):
   pass
 

This will be really efficient actually, since it you have two expressions that depends on a shared calculation, it will execute that twice. It will be more efficient to use:

for i, row in df['x', 'y'].iterrrows():
  print(row['x'], row['y'])

However, I really like the idea of using chunks! iterrows doesn't use that. Is it an idea to merge these ideas, and document them in the tutorial (@JovanVeljanoski ?)