[SOLVED] Assign a value to a single SFrame element

Assign a value to a single SFrame element

I want to assign a value to a single element (i.e. single row and column) in an SFrame. I am using the Python Notebook and importing graphlab.

I created an SFrame with dimensions 16364 rows x 37 columns. The column 'test' contains zeros.

I have used the following syntax to set the value: sf[1]['test'] = 3;

If I then type: sf[1]['test']

then I see the correct value, i.e "3"

But if I type: sf

then I just see values of zero for all rows of column 'test'

Also same for sf.head() or sf['test'] or sf['test'].head()

I don't understand why one syntax shows the value of "3" where an alternative one does not. Is the value in sf[1]['test'] 3 or 0 ?

Solution

SFrames are immutable, so they don't actually support item assignment. The reason for the difference you see here is because

sf[1]['test']

isn't actually referring to the SFrame at all. "sf[1]" returns a dictionary with keys that match to the SFrame's column names, and values that match the second row of the SFrame. When you assign a number to "sf[1]['test']", you are changing the value of the "test" key in the dictionary that was returned, so the SFrame "sf" is not involved in the assignment. The correct way to reference only the second value of the column "test" and assign the value "3" is this:

sf['test'][1] = 3

which would return this error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-5-c52dab41d5dd> in <module>()
----> 1 sf['test'][1] = 3

TypeError: 'SArray' object does not support item assignment