import numpy as np

def get_cindex(Y, P):
    summ = 0
    pair = 0
    
    for i in range(1, len(Y)):
        for j in range(0, i):
            if i is not j:
                if(Y[i] > Y[j]):
                    pair +=1
                    summ +=  1* (P[i] > P[j]) + 0.5 * (P[i] == P[j])
        
            
    if pair is not 0:
        return summ/pair
    else:
        return 0


def r_squared_error(y_obs,y_pred):
    y_obs = np.array(y_obs)
    y_pred = np.array(y_pred)
    y_obs_mean = [np.mean(y_obs) for y in y_obs]
    y_pred_mean = [np.mean(y_pred) for y in y_pred]

    mult = sum((y_pred - y_pred_mean) * (y_obs - y_obs_mean))
    mult = mult * mult

    y_obs_sq = sum((y_obs - y_obs_mean)*(y_obs - y_obs_mean))
    y_pred_sq = sum((y_pred - y_pred_mean) * (y_pred - y_pred_mean) )

    return mult / float(y_obs_sq * y_pred_sq)


def get_k(y_obs,y_pred):
    y_obs = np.array(y_obs)
    y_pred = np.array(y_pred)

    return sum(y_obs*y_pred) / float(sum(y_pred*y_pred))


def squared_error_zero(y_obs,y_pred):
    k = get_k(y_obs,y_pred)

    y_obs = np.array(y_obs)
    y_pred = np.array(y_pred)
    y_obs_mean = [np.mean(y_obs) for y in y_obs]
    upp = sum((y_obs - (k*y_pred)) * (y_obs - (k* y_pred)))
    down= sum((y_obs - y_obs_mean)*(y_obs - y_obs_mean))

    return 1 - (upp / float(down))


def get_rm2(ys_orig,ys_line):
    r2 = r_squared_error(ys_orig, ys_line)
    r02 = squared_error_zero(ys_orig, ys_line)

    return r2 * (1 - np.sqrt(np.absolute((r2*r2)-(r02*r02))))