How do I create test and train samples from one dataframe with pandas?

Question

I have a fairly large dataset in the form of a dataframe and I was wondering how I would be able to split the dataframe into two random samples (80% and 20%) for training and testing.

Thanks!

Answer 1

I do this in 2 ways.
Method 1:

from sklearn.model_selection import train_test_split
#Split the dataset into X and y
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)

Method 2:

from sklearn.model_selection import train_test_split
#Split the dataset into X and y
X_train, X_test, y_train, y_test = train_test_split(X, y, train_size=0.8, random_state=42)

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Answer 2

That's what I do:

train_dataset = dataset.sample(frac=0.80, random_state=200)
val_dataset = dataset.drop(train_dataset.index).sample(frac=1.00, random_state=200, ignore_index = True).copy()
train_dataset = train_dataset.sample(frac=1.00, random_state=200, ignore_index = True).copy()
del dataset

Answer 3

Split df into train, validate, test. Given a df of augmented data, select only the dependent and independent columns. Assign 10% of most recent rows (using 'dates' column) to test_df. Randomly assign 10% of remaining rows to validate_df with rest being assigned to train_df. Do not reindex. Check that all rows are uniquely assigned. Use only native python and pandas libs.

Method 1: Split rows into train, validate, test dataframes.

train_df = augmented_df[dependent_and_independent_columns]
test_df = train_df.sort_values('dates').tail(int(len(augmented_df)*0.1)) # select latest 10% of dates for test data
train_df = train_df.drop(test_df.index) # drop rows assigned to test_df
validate_df = train_df.sample(frac=0.1) # randomly assign 10%
train_df = train_df.drop(validate_df.index) # drop rows assigned to validate_df
assert len(augmented_df) == len(set(train_df.index).union(validate_df.index).union(test_df.index)) # every row must be uniquely assigned to a df

Method 2: Split rows when validate must be subset of train (fastai)

train_validate_test_df = augmented_df[dependent_and_independent_columns]
test_df = train_validate_test_df.loc[augmented_df.sort_values('dates').tail(int(len(augmented_df)*0.1)).index] # select latest 10% of dates for test data
train_validate_df = train_validate_test_df.drop(test_df.index) # drop rows assigned to test_df
validate_df = train_validate_df.sample(frac=validate_ratio) # assign 10% to validate_df
train_df = train_validate_df.drop(validate_df.index) # drop rows assigned to validate_df
assert len(augmented_df) == len(set(train_df.index).union(validate_df.index).union(test_df.index)) # every row must be uniquely assigned to a df
# fastai example usage
dls = fastai.tabular.all.TabularDataLoaders.from_df(
train_validate_df, valid_idx=train_validate_df.index.get_indexer_for(validate_df.index))

Answer 4

Pandas random sample will also work

train=df.sample(frac=0.8,random_state=200)
test=df.drop(train.index)

For the same random_state value you will always get the same exact data in the training and test set. This brings in some level of repeatability while also randomly separating training and test data.

Answer 5

The sample method selects a part of data, you can shuffle the data first by passing a seed value.

train = df.sample(frac=0.8, random_state=42)

For test set you can drop the rows through indexes of train DF and then reset the index of new DF.

test = df.drop(train_data.index).reset_index(drop=True)

Answer 6

Scikit Learn's train_test_split is a good one. It will split both numpy arrays and dataframes.

from sklearn.model_selection import train_test_split

train, test = train_test_split(df, test_size=0.2)

Answer 7

I would use K-fold cross validation. It's been proven to give much better results than the train_test_split Here's an article on how to apply it with sklearn from the documentation itself: https://scikit-learn.org/stable/modules/generated/sklearn.model_selection.KFold.html

Answer 8

if you want to split it to train, test and validation set you can use this function:

from sklearn.model_selection import train_test_split
import pandas as pd

def train_test_val_split(df, test_size=0.15, val_size=0.45):
    temp, test = train_test_split(df, test_size=test_size)
    total_items_count = len(df.index)
    val_length = total_items_count * val_size
    new_val_propotion = val_length / len(temp.index) 
    train, val = train_test_split(temp, test_size=new_val_propotion)
    return train, test, val

Answer 9

No need to convert to numpy. Just use a pandas df to do the split and it will return a pandas df.

from sklearn.model_selection import train_test_split

train, test = train_test_split(df, test_size=0.2)

And if you want to split x from y

X_train, X_test, y_train, y_test = train_test_split(df[list_of_x_cols], df[y_col],test_size=0.2)

And if you want to split the whole df

X, y = df[list_of_x_cols], df[y_col]

Answer 10

In my case, I wanted to split a data frame in Train, test and dev with a specific number. Here I am sharing my solution

First, assign a unique id to a dataframe (if already not exist)

import uuid
df['id'] = [uuid.uuid4() for i in range(len(df))]

Here are my split numbers:

train = 120765
test  = 4134
dev   = 2816

The split function

def df_split(df, n):
    
    first  = df.sample(n)
    second = df[~df.id.isin(list(first['id']))]
    first.reset_index(drop=True, inplace = True)
    second.reset_index(drop=True, inplace = True)
    return first, second

Now splitting into train, test, dev

train, test = df_split(df, 120765)
test, dev   = df_split(test, 4134)

Answer 11

shuffle = np.random.permutation(len(df))
test_size = int(len(df) * 0.2)
test_aux = shuffle[:test_size]
train_aux = shuffle[test_size:]
TRAIN_DF =df.iloc[train_aux]
TEST_DF = df.iloc[test_aux]

Answer 12

I would use scikit-learn's own training_test_split, and generate it from the index

from sklearn.model_selection import train_test_split


y = df.pop('output')
X = df

X_train,X_test,y_train,y_test = train_test_split(X.index,y,test_size=0.2)
X.iloc[X_train] # return dataframe train

Answer 13

you need to convert pandas dataframe into numpy array and then convert numpy array back to dataframe

 import pandas as pd
df=pd.read_csv('/content/drive/My Drive/snippet.csv', sep='\t')
from sklearn.model_selection import train_test_split

train, test = train_test_split(df, test_size=0.2)
train1=pd.DataFrame(train)
test1=pd.DataFrame(test)
train1.to_csv('/content/drive/My Drive/train.csv',sep="\t",header=None, encoding='utf-8', index = False)
test1.to_csv('/content/drive/My Drive/test.csv',sep="\t",header=None, encoding='utf-8', index = False)

Answer 14

To split into more than two classes such as train, test, and validation, one can do:

probs = np.random.rand(len(df))
training_mask = probs < 0.7
test_mask = (probs>=0.7) & (probs < 0.85)
validatoin_mask = probs >= 0.85


df_training = df[training_mask]
df_test = df[test_mask]
df_validation = df[validatoin_mask]

This will put approximately 70% of data in training, 15% in test, and 15% in validation.

Answer 15

You can use ~ (tilde operator) to exclude the rows sampled using df.sample(), letting pandas alone handle sampling and filtering of indexes, to obtain two sets.

train_df = df.sample(frac=0.8, random_state=100)
test_df = df[~df.index.isin(train_df.index)]

Answer 16

There are many great answers above so I just wanna add one more example in the case that you want to specify the exact number of samples for the train and test sets by using just the numpy library.

# set the random seed for the reproducibility
np.random.seed(17)

# e.g. number of samples for the training set is 1000
n_train = 1000

# shuffle the indexes
shuffled_indexes = np.arange(len(data_df))
np.random.shuffle(shuffled_indexes)

# use 'n_train' samples for training and the rest for testing
train_ids = shuffled_indexes[:n_train]
test_ids = shuffled_indexes[n_train:]

train_data = data_df.iloc[train_ids]
train_labels = labels_df.iloc[train_ids]

test_data = data_df.iloc[test_ids]
test_labels = data_df.iloc[test_ids]

Answer 17

There are many ways to create a train/test and even validation samples.

Case 1: classic way train_test_split without any options:

from sklearn.model_selection import train_test_split
train, test = train_test_split(df, test_size=0.3)

Case 2: case of a very small datasets (<500 rows): in order to get results for all your lines with this cross-validation. At the end, you will have one prediction for each line of your available training set.

from sklearn.model_selection import KFold
kf = KFold(n_splits=10, random_state=0)
y_hat_all = []
for train_index, test_index in kf.split(X, y):
    reg = RandomForestRegressor(n_estimators=50, random_state=0)
    X_train, X_test = X[train_index], X[test_index]
    y_train, y_test = y[train_index], y[test_index]
    clf = reg.fit(X_train, y_train)
    y_hat = clf.predict(X_test)
    y_hat_all.append(y_hat)

Case 3a: Unbalanced datasets for classification purpose. Following the case 1, here is the equivalent solution:

from sklearn.model_selection import train_test_split
X_train, X_test, y_train, y_test = train_test_split(X, y, stratify=y, test_size=0.3)

Case 3b: Unbalanced datasets for classification purpose. Following the case 2, here is the equivalent solution:

from sklearn.model_selection import StratifiedKFold
kf = StratifiedKFold(n_splits=10, random_state=0)
y_hat_all = []
for train_index, test_index in kf.split(X, y):
    reg = RandomForestRegressor(n_estimators=50, random_state=0)
    X_train, X_test = X[train_index], X[test_index]
    y_train, y_test = y[train_index], y[test_index]
    clf = reg.fit(X_train, y_train)
    y_hat = clf.predict(X_test)
    y_hat_all.append(y_hat)

Case 4: you need to create a train/test/validation sets on big data to tune hyperparameters (60% train, 20% test and 20% val).

from sklearn.model_selection import train_test_split
X_train, X_test_val, y_train, y_test_val = train_test_split(X, y, test_size=0.6)
X_test, X_val, y_test, y_val = train_test_split(X_test_val, y_test_val, stratify=y, test_size=0.5)

Answer 18

A bit more elegant to my taste is to create a random column and then split by it, this way we can get a split that will suit our needs and will be random.

def split_df(df, p=[0.8, 0.2]):
import numpy as np
df["rand"]=np.random.choice(len(p), len(df), p=p)
r = [df[df["rand"]==val] for val in df["rand"].unique()]
return r

Answer 19

import pandas as pd

from sklearn.model_selection import train_test_split

datafile_name = 'path_to_data_file'

data = pd.read_csv(datafile_name)

target_attribute = data['column_name']

X_train, X_test, y_train, y_test = train_test_split(data, target_attribute, test_size=0.8)

Answer 20

You can use below code to create test and train samples :

from sklearn.model_selection import train_test_split
trainingSet, testSet = train_test_split(df, test_size=0.2)

Test size can vary depending on the percentage of data you want to put in your test and train dataset.

Answer 21

If you need to split your data with respect to the lables column in your data set you can use this:

def split_to_train_test(df, label_column, train_frac=0.8):
    train_df, test_df = pd.DataFrame(), pd.DataFrame()
    labels = df[label_column].unique()
    for lbl in labels:
        lbl_df = df[df[label_column] == lbl]
        lbl_train_df = lbl_df.sample(frac=train_frac)
        lbl_test_df = lbl_df.drop(lbl_train_df.index)
        print '\n%s:\n---------\ntotal:%d\ntrain_df:%d\ntest_df:%d' % (lbl, len(lbl_df), len(lbl_train_df), len(lbl_test_df))
        train_df = train_df.append(lbl_train_df)
        test_df = test_df.append(lbl_test_df)

    return train_df, test_df

and use it:

train, test = split_to_train_test(data, 'class', 0.7)

you can also pass random_state if you want to control the split randomness or use some global random seed.

Answer 22

Just select range row from df like this

row_count = df.shape[0]
split_point = int(row_count*1/5)
test_data, train_data = df[:split_point], df[split_point:]

Answer 23

There are many valid answers. Adding one more to the bunch. from sklearn.cross_validation import train_test_split

#gets a random 80% of the entire set
X_train = X.sample(frac=0.8, random_state=1)
#gets the left out portion of the dataset
X_test = X.loc[~df_model.index.isin(X_train.index)]

Answer 24

How about this? df is my dataframe

total_size=len(df)

train_size=math.floor(0.66*total_size) (2/3 part of my dataset)

#training dataset
train=df.head(train_size)
#test dataset
test=df.tail(len(df) -train_size)

Answer 25

You can make use of df.as_matrix() function and create Numpy-array and pass it.

Y = df.pop()
X = df.as_matrix()
x_train, x_test, y_train, y_test = train_test_split(X, Y, test_size = 0.2)
model.fit(x_train, y_train)
model.test(x_test)

Answer 26

I think you also need to a get a copy not a slice of dataframe if you wanna add columns later.

msk = np.random.rand(len(df)) < 0.8
train, test = df[msk].copy(deep = True), df[~msk].copy(deep = True)

Answer 27

If your wish is to have one dataframe in and two dataframes out (not numpy arrays), this should do the trick:

def split_data(df, train_perc = 0.8):

   df['train'] = np.random.rand(len(df)) < train_perc

   train = df[df.train == 1]

   test = df[df.train == 0]

   split_data ={'train': train, 'test': test}

   return split_data

Answer 28

This is what I wrote when I needed to split a DataFrame. I considered using Andy's approach above, but didn't like that I could not control the size of the data sets exactly (i.e., it would be sometimes 79, sometimes 81, etc.).

def make_sets(data_df, test_portion):
    import random as rnd

    tot_ix = range(len(data_df))
    test_ix = sort(rnd.sample(tot_ix, int(test_portion * len(data_df))))
    train_ix = list(set(tot_ix) ^ set(test_ix))

    test_df = data_df.ix[test_ix]
    train_df = data_df.ix[train_ix]

    return train_df, test_df


train_df, test_df = make_sets(data_df, 0.2)
test_df.head()

Answer 29

You may also consider stratified division into training and testing set. Startified division also generates training and testing set randomly but in such a way that original class proportions are preserved. This makes training and testing sets better reflect the properties of the original dataset.

import numpy as np  

def get_train_test_inds(y,train_proportion=0.7):
    '''Generates indices, making random stratified split into training set and testing sets
    with proportions train_proportion and (1-train_proportion) of initial sample.
    y is any iterable indicating classes of each observation in the sample.
    Initial proportions of classes inside training and 
    testing sets are preserved (stratified sampling).
    '''

    y=np.array(y)
    train_inds = np.zeros(len(y),dtype=bool)
    test_inds = np.zeros(len(y),dtype=bool)
    values = np.unique(y)
    for value in values:
        value_inds = np.nonzero(y==value)[0]
        np.random.shuffle(value_inds)
        n = int(train_proportion*len(value_inds))

        train_inds[value_inds[:n]]=True
        test_inds[value_inds[n:]]=True

    return train_inds,test_inds

df[train_inds] and df[test_inds] give you the training and testing sets of your original DataFrame df.

Answer 30

I would just use numpy's randn:

In [11]: df = pd.DataFrame(np.random.randn(100, 2))

In [12]: msk = np.random.rand(len(df)) < 0.8

In [13]: train = df[msk]

In [14]: test = df[~msk]

And just to see this has worked:

In [15]: len(test)
Out[15]: 21

In [16]: len(train)
Out[16]: 79