The video, notebooks, spreadsheets, and links are available here.

# Lesson 4 discussion

**lin.crampton**(lin.crampton) #2

Embedding - In lesson4, under the Dot Product section, Embedding is called to try to create an embedding layer.

u = Embedding(n_users, n_factors, input_length=1, W_regularizer=l2(1e-5))(user_in)

It gives me a NameError and I am not sure how to fix it. I donât know if it is a setup problem on my side (I set up my own server) or where I should be looking to fix this problem. I did a %whos and Embedding is not in my environment. Any suggestions on where I should go from here âŚ

-=-=-

user_in = Input(shape=(1,), dtype=âint64â, name=âuser_inâ)

u = Embedding(n_users, n_factors, input_length=1, W_regularizer=l2(1e-5))(user_in)

movie_in = Input(shape=(1,), dtype=âint64â, name=âmovie_inâ)

m = Embedding(n_movies, n_factors, input_length=1, W_regularizer=l2(1e-5))(movie_in)

NameError Traceback (most recent call last)

in ()

1 user_in = Input(shape=(1,), dtype=âint64â, name=âuser_inâ)

----> 2 u = Embedding(n_users, n_factors, input_length=1, W_regularizer=l2(1e-5))(user_in)

3 movie_in = Input(shape=(1,), dtype=âint64â, name=âmovie_inâ)

4 m = Embedding(n_movies, n_factors, input_length=1, W_regularizer=l2(1e-5))(movie_in)

NameError: name âEmbeddingâ is not defined

## -=-=-

%whos

Variable Type Data/Info

Adam type <class âkeras.optimizers.Adamâ>

BatchNormalization type <class âkeras.layers.norm<âŚ>tion.BatchNormalizationâ>

Convolution2D type <class âkeras.layers.conv<âŚ>olutional.Convolution2Dâ>

Dense type <class âkeras.layers.core.Denseâ>

Dropout type <class âkeras.layers.core.Dropoutâ>

Flatten type <class âkeras.layers.core.Flattenâ>

GlobalAveragePooling2D type <class âkeras.layers.pool<âŚ>.GlobalAveragePooling2Dâ>

Image module <module âPIL.Imageâ from <âŚ>-packages/PIL/Image.pycâ>

Input function <function Input at 0x7f7aba5652a8>

K module <module âkeras.backendâ f<âŚ>as/backend/**init**.pycâ>

.

.

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**jeremy**(Jeremy Howard (Admin)) #3

Thanks for the question. According to the docs, the full name is âkeras.layers.embeddings.Embeddingâ. Therefore you can either refer to it by its full name everywhere you use it (which you probably donât want to do!), or you can add to the top of your notebook:

```
from keras.layers.embeddings import Embedding
```

Or you can add that line to utils.py and reload it.

Hereâs some more information about how python handles this.

**lin.crampton**(lin.crampton) #4

Thanks, Jeremy. That worked. Glad its not a sign of something inherently wrong with my setup.

**chris**(chris) #5

Lesson 4 reminded me of a âFactor analysisâ I saw in a recent paper:

Source: http://www.foodandnutritionresearch.net/index.php/fnr/article/view/31694

Is this not very similar to the Koren et al chart @rachel posted in Slack?

**jeremy**(Jeremy Howard (Admin)) #6

Somewhat similar, yes. Factor analysis / principal components analysis are linear methods that create a lower dimensional matrix that attempts to capture the variance in the original matrix, just like our model did. If you want to read more, search for âPCAâ and âfactor analysisâ for the classic methods like you show, and âprobabilistic matrix factorizationâ for the approach we used in class.

**chris**(chris) #8

I tried the lesson 4 notebook using my own data:

30,746 total features taken from my database of blood tests, urinary organic acids and hormone metabolites. 447 unique users and 208 unique markers. I normalised everything using `sklearn.preprocessing.scale`

.

I reduced the number of latent factors to 5 and he rest of the notebook is as you presented it.

`val_loss: 0.9314`

Iâm very excited about the idea of being able to describe my users with just five latent factors. Iâm even more excited about scatter plotting the markers using their top latent factors because I think the plot will make physiological sense in the same way as the scatter plot for movies makes sense.

My question is, where did the latent factors in the Keras model go?

```
model.fit([trn.userId, trn.marker], trn.result, batch_size=64, nb_epoch=10,
validation_data=([val.userId, val.marker], val.result))
trn.result.shape
(24466,)
```

The users and markers were concatenated to form the input, do I need to split them back up to get my latent factors?

**jeremy**(Jeremy Howard (Admin)) #11

Warning - some of the code in that project is not too niceâŚ!

**chris**(chris) #12

Did you notice who he is? âChief Architect at Elsevier, the worldâs leading scientific publisher.â

**janardhanp22**(janardhanp22) #13

@jeremy By the method of collaborative filtering, we need to predict the missing ratings right?

In the spreadsheet case: MovieId : 49 UserId: 212

result is 0.0 in the spreadsheet. Are we not supposed to predict this unknown rating, am I missing anything here ?

**jeremy**(Jeremy Howard (Admin)) #14

At training time (which is shown in the spreadsheets) we predict the rating for those which are labeled, so that we can compare to the true labels and calculate the value of the loss function. So we donât predict the rating you mention, since we donât have a label for it in the training set.

**janardhanp22**(janardhanp22) #15

Just curious, how do we predict MovieId : 49 UserId: 212 value at test time ?

**vshets**(vedshetty) #16

At this point: https://youtu.be/V2h3IOBDvrA?t=10m56s did @jeremy by any chance mean sigmoid is the activation function as opposed to loss function?

**janardhanp22**(janardhanp22) #18

@jeremy I was able to solve the book-crossing dataset recommendation using similar architecture as taught in the class.

Below are results on a sample of 60k data points. Need to tune still since val loss is increasingâŚ

Train on 48036 samples, validate on 11962 samples

Epoch 1/5

48036/48036 [==============================] - 34s - loss: 14.5920 - val_loss: 12.4964

Epoch 2/5

48036/48036 [==============================] - 46s - loss: 8.5997 - val_loss: 13.8392

Epoch 3/5

48036/48036 [==============================] - 78s - loss: 5.2262 - val_loss: 14.6633

Epoch 4/5

48036/48036 [==============================] - 78s - loss: 4.3011 - val_loss: 14.7733

Epoch 5/5

48036/48036 [==============================] - 79s - loss: 3.8658 - val_loss: 14.7772

Out[19]:

**ccrome**(Caleb Crome) #20

Hi All,

My buddy pointed me to this course a couple weeks ago, and Iâm now totally obsessed with deep learning & neural networks. Thanks to everybody working on this course!

Anyway, Iâm working through the homework, and I have a practical question about the embeddings: once a model is trained and set up, how do you add new users and new movies to the database?

Since the embeddings take as an input the number of users and number of movies as inputs (and create parameters accordingly), it seems the model is locked down to those movies and users.

Are there clever ways to modify the layers to include extra movies and users, or do you need to retrain from scratch every time you add new data?

Thanks,

-Caleb