Tree recursion on python

Question

I have the following tree algorithm which prints the conditions for each leaf:

def _grow_tree(self, X, y, depth=0):
    # Identify best split
    idx, thr = self._best_split(X, y)

    # Indentation for tree description
    indent = "    " * depth

    indices_left = X.iloc[:, idx] < thr
    X_left = X[indices_left]
    y_left = y_train[X_left.reset_index().loc[:,'id'].values]

    X_right = X[~indices_left]
    y_right = y_train[X_right.reset_index().loc[:,'id'].values]

    self.tree_describe.append(indent +"if x['"+ X.columns[idx] + "'] <= " +\
                             str(thr) + ':')
    # Grow on left side of the tree  
    node.left = self._grow_tree(X_left, y_left, depth + 1)

    self.tree_describe.append(indent +"else: #if x['"+ X.columns[idx] + "'] > " +\
                         str(thr) + ':')
    # Grow on right side of the tree
    node.right = self._grow_tree(X_right, y_right, depth + 1)

    return node

This produces the following print for a particular case:

["if x['VAR1'] <= 0.5:",
 "    if x['VAR2'] <= 0.5:",
 "    else: #if x['VAR2'] > 0.5:",
 "else: #if x['VAR1'] > 0.5:",
 "    if x['VAR3'] <= 0.5:",
 "    else: #if x['VAR3'] > 0.5:"]

How could I obtain the following output?:

["if x['VAR1'] <= 0.5:",
 "    if x['VAR1'] <= 0.5&x['VAR2'] <= 0.5",
 "    else: #if x['VAR1'] <= 0.5&x['VAR2'] > 0.5:",
 "else: #if x['VAR1'] > 0.5:",
 "    if x['VAR1'] > 0.5&x['VAR3'] <= 0.5:",
 "    else: #if x['VAR1'] > 0.5&x['VAR3'] > 0.5:"]

Didn't you make the indentation because you didn't want this output? Because now indent shows which item is a child of another, and now you want to repeat the x['VAR1'] <= 0.5/x['VAR1'] > 0.5 parts to show that. — h4z3
– h4z3, Commented Feb 25, 2020 at 14:59
Initially yes, but now I intend to use the pandas query function to create leaf columns based on conditions and the first way is not practical. I need for each leaf to have all the conditions. — Jojo
– Jojo, Commented Feb 25, 2020 at 15:07
So just forward it like you did with depth. Depth grows +1, description elements will grow with conditions. — h4z3
– h4z3, Commented Feb 25, 2020 at 15:25

trincot · Accepted Answer · 2020-02-25 15:09:11Z

1

You could introduce a new argument to your function, which will have the string with higher-level condition(s) that need to be added to each deeper conditions:

I would also suggest using .format() for your string building:

def _grow_tree(self, X, y, depth=0, descr=""):

    idx, thr = self._best_split(X, y)

    indent = "    " * depth

    cond = "x['{}'] <= {}{}".format(X.columns[idx], thr, descr)
    self.tree_describe.append("{}if {}:".format(indent, cond))

    node.left = self._grow_tree(X_left, y_left, depth + 1, " & " + cond)

    cond = "x['{}'] > {}{}".format(X.columns[idx], thr, descr)
    self.tree_describe.append("{}else: #if {}:".format(indent, cond))

    node.right = self._grow_tree(X_right, y_right, depth + 1, " & " + cond)

    return node

answered Feb 25, 2020 at 15:09

trincot

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